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Appendix G – Crosscutting Concepts
Crosscutting concepts have value because they provide students with connections
and intellectual tools that are related across the differing areas of disciplinary
content and can enrich their application of practices and their understanding of core
ideas. — Framework p. 233
A Framework for K-12 Science Education: Practices, Core Ideas, and Crosscutting Concepts
(Framework) recommends science education in grades K-12 be built around three major
dimensions: scientific and engineering practices; crosscutting concepts that unify the study of
science and engineering through their common application across fields; and core ideas in the major
disciplines of natural science. The purpose of this appendix is to describe the second dimension—
crosscutting concepts—and to explain its role in the Next Generation Science Standards (NGSS).
The Framework identifies seven crosscutting concepts that bridge disciplinary boundaries, uniting
core ideas throughout the fields of science and engineering. Their purpose is to help students deepen
their understanding of the disciplinary core ideas (pp. 2 and 8), and develop a coherent and
scientifically based view of the world (p. 83.) The seven crosscutting concepts presented in Chapter
4 of the Framework are as follows:
1. Patterns. Observed patterns of forms and events guide organization and classification, and
they prompt questions about relationships and the factors that influence them.
2. Cause and effect: Mechanism and explanation. Events have causes, sometimes simple,
sometimes multifaceted. A major activity of science is investigating and explaining causal
relationships and the mechanisms by which they are mediated. Such mechanisms can then be
tested across given contexts and used to predict and explain events in new contexts.
3. Scale, proportion, and quantity. In considering phenomena, it is critical to recognize what is
relevant at different measures of size, time, and energy and to recognize how changes in scale,
proportion, or quantity affect a system’s structure or performance.
4. Systems and system models. Defining the system under study—specifying its boundaries and
making explicit a model of that system—provides tools for understanding and testing ideas that
are applicable throughout science and engineering.
5. Energy and matter: Flows, cycles, and conservation. Tracking fluxes of energy and matter
into, out of, and within systems helps one understand the systems’ possibilities and limitations.
6. Structure and function. The way in which an object or living thing is shaped and its
substructure determine many of its properties and functions.
7. Stability and change. For natural and built systems alike, conditions of stability and
determinants of rates of change or evolution of a system are critical elements of study.
The Framework notes that crosscutting concepts are featured prominently in other documents about
what all students should learn about science for the past two decades. These have been called
“themes” in Science for All Americans (AAA 1989) and Benchmarks for Science Literacy (1993),
“unifying principles” in National Science Education Standards (1996), and “crosscutting ideas”
NSTA’s Science Anchors Project (2010). Although these ideas have been consistently included in
previous standards documents the Framework recognizes that “students have often been expected to
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build such knowledge without any explicit instructional support. Hence the purpose of highlighting
them as Dimension 2 of the framework is to elevate their role in the development of standards,
curricula, instruction, and assessments.” (p. 83) The writing team has continued this commitment by
weaving crosscutting concepts into the performance expectations for all students—so they cannot
be left out.
Guiding Principles
The Framework recommended crosscutting concepts be embedded in the science curriculum
beginning in the earliest years of schooling and suggested a number of guiding principles for how
they should be used. The development process of the standards provided insights into the
crosscutting concepts. These insights are shared in the following guiding principles.
Crosscutting concepts can help students better understand core ideas in science and
engineering. When students encounter new phenomena, whether in a science lab, field trip, or on
their own, they need mental tools to help engage in and come to understand the phenomena from a
scientific point of view. Familiarity with crosscutting concepts can provide that perspective. For
example, when approaching a complex phenomenon (either a natural phenomenon or a machine) an
approach that makes sense is to begin by observing and characterizing the phenomenon in terms of
patterns. A next step might be to simplify the phenomenon by thinking of it as a system and
modeling its components and how they interact. In some cases it would be useful to study how
energy and matter flow through the system, or to study how structure affects function (or
malfunction). These preliminary studies may suggest explanations for the phenomena, which could
be checked by predicting patterns that might emerge if the explanation is correct, and matching
those predictions with those observed in the real world.
Crosscutting concepts can help students better understand science and engineering practices.
Because the crosscutting concepts address the fundamental aspects of nature, they also inform the
way humans attempt to understand it. Different crosscutting concepts align with different practices,
and when students carry out these practices, they are often addressing one of these crosscutting
concepts. For example, when students analyze and interpret data, they are often looking for patterns
in observations, mathematical or visual. The practice of planning and carrying out an investigation
is often aimed at identifying cause and effect relationships: if you poke or prod something, what
will happen? The crosscutting concept of “Systems and System Models” is clearly related to the
practice of developing and using models.
Repetition in different contexts will be necessary to build familiarity. Repetition is counter to
the guiding principles the writing team used in creating performance expectations to reflect the core
ideas in the science disciplines. In order to reduce the total amount of material students are held
accountable to learn, repetition was reduced whenever possible. However, crosscutting concepts are
repeated within grades at the elementary level and grade-bands at the middle and high school levels
so these concepts “become common and familiar touchstones across the disciplines and grade
levels.” (p. 83)
Crosscutting concepts should grow in complexity and sophistication across the grades.
Repetition alone is not sufficient. As students grow in their understanding of the science disciplines,
depth of understanding crosscutting concepts should grow as well. The writing team has adapted
and added to the ideas expressed in the Framework in developing a matrix for use in crafting
performance expectations that describe student understanding of the crosscutting concepts. The
matrix is found at the end of this section.
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Crosscutting concepts can provide a common vocabulary for science and engineering. The
practices, disciplinary core ideas, and crosscutting concepts are the same in science and
engineering. What is different is how and why they are used—to explain natural phenomena in
science, and to solve a problem or accomplish a goal in engineering. Students need both types of
experiences to develop a deep and flexible understanding of how these terms are applied in each of
these closely allied fields. As crosscutting concepts are encountered repeatedly across academic
disciplines, familiar vocabulary can enhance engagement and understanding for English language
learners, students with language processing difficulties, and students with limited literacy
development.
Crosscutting concepts should not be assessed separately from practices or core ideas. Students
should not be assessed on their ability to define “pattern,” “system,” or any other crosscutting
concepts as a separate vocabulary word. To capture the vision in the Framework, students should be
assessed on the extent to which they have achieved a coherent scientific worldview by recognizing
similarities among core ideas in science or engineering that may at first seem very different, but are
united through crosscutting concepts.
Performance expectations focus on some but not all capabilities associated with a crosscutting
concept. As core ideas grow in complexity and sophistication across the grades it becomes more
and more difficult to express them fully in performance expectations. Consequently, most
performance expectations reflect only some aspects of a crosscutting concept. These aspects are
indicated in the right-hand foundation box in each of the standards. All aspects of each core idea
considered by the writing team can be found in the matrix at the end of this section.
Crosscutting concepts are for all students. Crosscutting concepts raise the bar for students who
have not achieved at high levels in academic subjects and often assigned to classes that emphasize
“the basics,” which in science may be taken to provide primarily factual information and lower-
order thinking skills. Consequently, it is essential that all students engage in using crosscutting
concepts, which could result in leveling the playing field and promoting deeper understanding for
all students.
Inclusion of Nature of Science and Engineering Concepts. Sometimes included in the
crosscutting concept foundation boxes are concepts related to materials from the “Nature of
Science” or “Science, Technology, Society, and the Environment.” These are not to be confused
with the “Crosscutting Concepts” but rather represent an organizational structure of the NGSS
recognizing concepts from both the Nature of Science and Science, Technology, Society, and the
Environment that extend across all of the sciences. Readers should use Appendices H and J for
further information on these ideas.
Progression of Crosscutting Concepts Across the Grades
Following is a brief summary of how each crosscutting concept increases in complexity and
sophistication across the grades as envisioned in the Framework. Examples of performance
expectations illustrate how these ideas play out in the NGSS.
1. “Patterns exist everywhere—in regularly occurring shapes or structures and in repeating events
and relationships. For example, patterns are discernible in the symmetry of flowers and snowflakes,
the cycling of the seasons, and the repeated base pairs of DNA.” (p. 85)
While there are many patterns in nature, they are not the norm since there is a tendency for disorder
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to increase (e.g. it is far more likely for a broken glass to scatter than for scattered bits to assemble
themselves into a whole glass). In some cases, order seems to emerge from chaos, as when a plant
sprouts, or a tornado appears amidst scattered storm clouds. It is in such examples that patterns exist
and the beauty of nature is found. “Noticing patterns is often a first step to organizing phenomena
and asking scientific questions about why and how the patterns occur.” (p. 85)
“Once patterns and variations have been noted, they lead to questions; scientists seek explanations
for observed patterns and for the similarity and diversity within them. Engineers often look for and
analyze patterns, too. For example, they may diagnose patterns of failure of a designed system
under test in order to improve the design, or they may analyze patterns of daily and seasonal use of
power to design a system that can meet the fluctuating needs.” (page 85-86)
Patterns figure prominently in the science and engineering practice of “Analyzing and Interpreting
Data.” Recognizing patterns is a large part of working with data. Students might look at
geographical patterns on a map, plot data values on a chart or graph, or visually inspect the
appearance of an organism or mineral. The crosscutting concept of patterns is also strongly
associated with the practice of “Using Mathematics and Computational Thinking.” It is often the
case that patterns are identified best using mathematical concepts. As Richard Feynman said, “To
those who do not know mathematics it is difficult to get across a real feeling as to the beauty, the
deepest beauty, of nature. If you want to learn about nature, to appreciate nature, it is necessary to
understand the language that she speaks in.”
The human brain is remarkably adept at identifying patterns, and students progressively build upon
this innate ability throughout their school experiences. The following table lists the guidelines used
by the writing team for how this progression plays out across K-12, with examples of performance
expectations drawn from the NGSS.
Progression Across the Grades
Performance Expectation from the NGSS
In grades K-2, children recognize that patterns in the natural
and human designed world can be observed, used to describe
phenomena, and used as evidence.
1-ESS1-1. Use observations of the sun, moon, and
stars to describe patterns that can be predicted.
In grades 3-5, students identify similarities and differences
in order to sort and classify natural objects and designed
products. They identify patterns related to time, including
simple rates of change and cycles, and to use these patterns
to make predictions.
4-PS4-1. Develop a model of waves to describe
patterns in terms of amplitude and wavelength and
that waves can cause objects to move.
In grades 6-8, students recognize that macroscopic patterns
are related to the nature of microscopic and atomic-level
structure. They identify patterns in rates of change and other
numerical relationships that provide information about
natural and human designed systems. They use patterns to
identify cause and effect relationships, and use graphs and
charts to identify patterns in data.
MS-LS4-1. Analyze and interpret data for patterns
in the fossil record that document the existence,
diversity, extinction, and change of life forms
throughout the history of life on Earth under the
assumption that natural laws operate today as in the
past.
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In grades 9-12, students observe patterns in systems at
different scales and cite patterns as empirical evidence for
causality in supporting their explanations of phenomena.
They recognize classifications or explanations used at one
scale may not be useful or need revision using a different
scale; thus requiring improved investigations and
experiments. They use mathematical representations to
identify certain patterns and analyze patterns of performance
in order to reengineer and improve a designed system.
HS-PS1-2. Construct and revise an explanation for
the outcome of a simple chemical reaction based on
the outermost electron states of atoms, trends in the
periodic table, and knowledge of the patterns of
chemical properties.
2. Cause and effect is often the next step in science, after a discovery of patterns or events that
occur together with regularity. A search for the underlying cause of a phenomenon has sparked
some of the most compelling and productive scientific investigations. “Any tentative answer, or
‘hypothesis,’ that A causes B requires a model or mechanism for the chain of interactions that
connect A and B. For example, the notion that diseases can be transmitted by a person’s touch was
initially treated with skepticism by the medical profession for lack of a plausible mechanism. Today
infectious diseases are well understood as being transmitted by the passing of microscopic
organisms (bacteria or viruses) between an infected person and another. A major activity of science
is to uncover such causal connections, often with the hope that understanding the mechanisms will
enable predictions and, in the case of infectious diseases, the design of preventive measures,
treatments, and cures.” (p. 87)
“In engineering, the goal is to design a system to cause a desired effect, so cause-and-effect
relationships are as much a part of engineering as of science. Indeed, the process of design is a good
place to help students begin to think in terms of cause and effect, because they must understand the
underlying causal relationships in order to devise and explain a design that can achieve a specified
objective.” (p.88)
When students perform the practice of “Planning and Carrying Out Investigations,” they often
address cause and effect. At early ages, this involves “doing” something to the system of study and
then watching to see what happens. At later ages, experiments are set up to test the sensitivity of the
parameters involved, and this is accomplished by making a change (cause) to a single component of
a system and examining, and often quantifying, the result (effect). Cause and effect is also closely
associated with the practice of “Engaging in Argument from Evidence.” In scientific practice,
deducing the cause of an effect is often difficult, so multiple hypotheses may coexist. For example,
though the occurrence (effect) of historical mass extinctions of organisms, such as the dinosaurs, is
well established, the reason or reasons for the extinctions (cause) are still debated, and scientists
develop and debate their arguments based on different forms of evidence. When students engage in
scientific argumentation, it is often centered about identifying the causes of an effect.
Progression Across the Grades
Performance Expectation from the NGSS
In grades K-2, students learn that events have causes that
generate observable patterns. They design simple tests to
gather evidence to support or refute their own ideas about
causes.
1-PS4-3. Plan and conduct an investigation to
determine the effect of placing objects made with
different materials in the path of a beam of light.
In grades 3-5, students routinely identify and test causal
relationships and use these relationships to explain change.
They understand events that occur together with regularity
might or might not signify a cause and effect relationship.
4-ESS2-1. Make observations and/or measurements
to provide evidence of the effects of weathering or
the rate of erosion by water, ice, wind, or
vegetation.
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In grades 6-8, students classify relationships as causal or
correlational, and recognize that correlation does not
necessarily imply causation. They use cause and effect
relationships to predict phenomena in natural or designed
systems. They also understand that phenomena may have
more than one cause, and some cause and effect relationships
in systems can only be described using probability.
MS-PS1-4. Develop a model that predicts and
describes changes in particle motion, temperature,
and state of a pure substance when thermal energy
is added or removed.
In grades 9-12, students understand that empirical evidence
is required to differentiate between cause and correlation and
to make claims about specific causes and effects. They
suggest cause and effect relationships to explain and predict
behaviors in complex natural and designed systems. They
also propose causal relationships by examining what is
known about smaller scale mechanisms within the system.
They recognize changes in systems may have various causes
that may not have equal effects.
HS-LS3-2. Make and defend a claim based on
evidence that inheritable genetic variations may
result from: (1) new genetic combinations through
meiosis, (2) viable errors occurring during
replication, and/or (3) mutations caused by
environmental factors.
3. Scale, Proportion and Quantity are important in both science and engineering. These are
fundamental assessments of dimension that form the foundation of observations about nature.
Before an analysis of function or process can be made (the how or why), it is necessary to identify
the what. These concepts are the starting point for scientific understanding, whether it is of a total
system or its individual components. Any student who has ever played the game “twenty questions”
understands this inherently, asking questions such as, “Is it bigger than a bread box?” in order to
first determine the object’s size.
An understanding of scale involves not only understanding systems and processes vary in size, time
span, and energy, but also different mechanisms operate at different scales. In engineering, “no
structure could be conceived, much less constructed, without the engineer’s precise sense of scale...
At a basic level, in order to identify something as bigger or smaller than something else—and how
much bigger or smaller—a student must appreciate the units used to measure it and develop a feel
for quantity.” (p. 90)
“The ideas of ratio and proportionality as used in science can extend and challenge students’
mathematical understanding of these concepts. To appreciate the relative magnitude of some
properties or processes, it may be necessary to grasp the relationships among different types of
quantities—for example, speed as the ratio of distance traveled to time taken, density as a ratio of
mass to volume. This use of ratio is quite different than a ratio of numbers describing fractions of a
pie. Recognition of such relationships among different quantities is a key step in forming
mathematical models that interpret scientific data.” (p. 90)
The crosscutting concept of Scale, Proportion, and Quantity figures prominently in the practices of
“Using Mathematics and Computational Thinking” and in “Analyzing and Interpreting Data.” This
concept addresses taking measurements of structures and phenomena, and these fundamental
observations are usually obtained, analyzed, and interpreted quantitatively. This crosscutting
concept also figures prominently in the practice of “Developing and Using Models.” Scale and
proportion are often best understood using models. For example, the relative scales of objects in the
solar system or of the components of an atom are difficult to comprehend mathematically (because
the numbers involved are either so large or so small), but visual or conceptual models make them
much more understandable (e.g., if the solar system were the size of a penny, the Milky Way galaxy
would be the size of Texas).
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Progression Across the Grades
Performance Expectation from the NGSS
In grades K-2, students use relative scales (e.g., bigger and
smaller; hotter and colder; faster and slower) to describe
objects. They use standard units to measure length.
In grades 3-5, students recognize natural objects and
observable phenomena exist from the very small to the
immensely large. They use standard units to measure and
describe physical quantities such as weight, time,
temperature, and volume.
5-ESS1-1. Support an argument that the apparent
brightness of the sun and stars is due to their relative
distances from Earth.
In grades 6-8, students observe time, space, and energy
phenomena at various scales using models to study systems
that are too large or too small. They understand phenomena
observed at one scale may not be observable at another scale,
and the function of natural and designed systems may change
with scale. They use proportional relationships (e.g., speed as
the ratio of distance traveled to time taken) to gather
information about the magnitude of properties and processes.
They represent scientific relationships through the use of
algebraic expressions and equations.
MS-LS1-1. Conduct an investigation to provide
evidence that living things are made of cells; either
one cell or many different numbers and types of
cells.
In grades 9-12, students understand the significance of a
phenomenon is dependent on the scale, proportion, and
quantity at which it occurs. They recognize patterns
observable at one scale may not be observable or exist at
other scales, and some systems can only be studied indirectly
as they are too small, too large, too fast, or too slow to
observe directly. Students use orders of magnitude to
understand how a model at one scale relates to a model at
another scale. They use algebraic thinking to examine
scientific data and predict the effect of a change in one
variable on another (e.g., linear growth vs. exponential
growth).
HS-ESS1-4. Use mathematical or computational
representations to predict the motion of orbiting
objects in the solar system.
4. Systems and System Models are useful in science and engineering because the world is
complex, so it is helpful to isolate a single system and construct a simplified model of it. “To do
this, scientists and engineers imagine an artificial boundary between the system in question and
everything else. They then examine the system in detail while treating the effects of things outside
the boundary as either forces acting on the system or flows of matter and energy across it—for
example, the gravitational force due to Earth on a book lying on a table or the carbon dioxide
expelled by an organism. Consideration of flows into and out of the system is a crucial element of
system design. In the laboratory or even in field research, the extent to which a system under study
can be physically isolated or external conditions controlled is an important element of the design of
an investigation and interpretation of results…The properties and behavior of the whole system can
be very different from those of any of its parts, and large systems may have emergent properties,
such as the shape of a tree, that cannot be predicted in detail from knowledge about the components
and their interactions.” (p. 92)
“Models can be valuable in predicting a system’s behaviors or in diagnosing problems or failures in
its functioning, regardless of what type of system is being examined… In a simple mechanical
system, interactions among the parts are describable in terms of forces among them that cause
changes in motion or physical stresses. In more complex systems, it is not always possible or useful
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to consider interactions at this detailed mechanical level, yet it is equally important to ask what
interactions are occurring (e.g., predator-prey relationships in an ecosystem) and to recognize that
they all involve transfers of energy, matter, and (in some cases) information among parts of the
system… Any model of a system incorporates assumptions and approximations; the key is to be
aware of what they are and how they affect the model’s reliability and precision. Predictions may be
reliable but not precise or, worse, precise but not reliable; the degree of reliability and precision
needed depends on the use to which the model will be put.” (p. 93)
Progression Across the Grades
Performance Expectation from the NGSS
In grades K-2, students understand objects and organisms
can be described in terms of their parts; and systems in the
natural and designed world have parts that work together.
K-ESS3-1. Use a model to represent the
relationship between the needs of different plants or
animals (including humans) and the places they live.
In grades 3-5, students understand that a system is a group
of related parts that make up a whole and can carry out
functions its individual parts cannot. They can also describe
a system in terms of its components and their interactions.
3-LS4-4. Make a claim about the merit of a
solution to a problem caused when the environment
changes and the types of plants and animals that live
there may change.
In grades 6-8, students can understand that systems may
interact with other systems; they may have sub-systems and
be a part of larger complex systems. They can use models to
represent systems and their interactions—such as inputs,
processes and outputs—and energy, matter, and information
flows within systems. They can also learn that models are
limited in that they only represent certain aspects of the
system under study.
MS-PS2-4. Construct and present arguments using
evidence to support the claim that gravitational
interactions are attractive and depend on the masses
of interacting objects.
In grades 9-12, students can investigate or analyze a system
by defining its boundaries and initial conditions, as well as
its inputs and outputs. They can use models (e.g., physical,
mathematical, computer models) to simulate the flow of
energy, matter, and interactions within and between systems
at different scales. They can also use models and simulations
to predict the behavior of a system, and recognize that these
predictions have limited precision and reliability due to the
assumptions and approximations inherent in the models.
They can also design systems to do specific tasks.
HS-LS2-5. Develop a model to illustrate the role of
photosynthesis and cellular respiration in the
cycling of carbon among the biosphere, atmosphere,
hydrosphere, and geosphere.
5. Energy and Matter are essential concepts in all disciplines of science and engineering, often in
connection with systems. “The supply of energy and of each needed chemical element restricts a
system’s operation—for example, without inputs of energy (sunlight) and matter (carbon dioxide
and water), a plant cannot grow. Hence, it is very informative to track the transfers of matter and
energy within, into, or out of any system under study.
“In many systems there also are cycles of various types. In some cases, the most readily observable
cycling may be of matter—for example, water going back and forth between Earth’s atmosphere
and its surface and subsurface reservoirs. Any such cycle of matter also involves associated energy
transfers at each stage, so to fully understand the water cycle, one must model not only how water
moves between parts of the system but also the energy transfer mechanisms that are critical for that
motion.
“Consideration of energy and matter inputs, outputs, and flows or transfers within a system or
process are equally important for engineering. A major goal in design is to maximize certain types
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of energy output while minimizing others, in order to minimize the energy inputs needed to achieve
a desired task.” (p. 95)
Progression Across the Grades
Performance Expectation from the NGSS
In grades K-2, students observe objects may break into
smaller pieces, be put together into larger pieces, or change
shapes.
2-PS1-3. Make observations to construct an
evidence-based account of how an object made of a
small set of pieces can be disassembled and made
into a new object.
In grades 3-5, students learn matter is made of particles and
energy can be transferred in various ways and between
objects. Students observe the conservation of matter by
tracking matter flows and cycles before and after processes
and recognizing the total weight of substances does not
change.
5-LS1-1. Support an argument that plants get the
materials they need for growth chiefly from air and
water.
In grades 6-8, students learn matter is conserved because
atoms are conserved in physical and chemical processes.
They also learn within a natural or designed system, the
transfer of energy drives the motion and/or cycling of matter.
Energy may take different forms (e.g. energy in fields,
thermal energy, energy of motion). The transfer of energy
can be tracked as energy flows through a designed or natural
system.
MS-ESS2-4. Develop a model to describe the
cycling of water through Earth’s systems driven by
energy from the sun and the force of gravity.
In grades 9-12, students learn that the total amount of energy
and matter in closed systems is conserved. They can
describe changes of energy and matter in a system in terms
of energy and matter flows into, out of, and within that
system. They also learn that energy cannot be created or
destroyed. It only moves between one place and another
place, between objects and/or fields, or between systems.
Energy drives the cycling of matter within and between
systems. In nuclear processes, atoms are not conserved, but
the total number of protons plus neutrons is conserved.
HS-PS1-8. Develop models to illustrate the changes
in the composition of the nucleus of the atom and
the energy released during the processes of fission,
fusion, and radioactive decay.
6. Structure and Function are complementary properties. “The shape and stability of structures of
natural and designed objects are related to their function(s). The functioning of natural and built
systems alike depends on the shapes and relationships of certain key parts as well as on the
properties of the materials from which they are made. A sense of scale is necessary in order to know
what properties and what aspects of shape or material are relevant at a particular magnitude or in
investigating particular phenomena—that is, the selection of an appropriate scale depends on the
question being asked. For example, the substructures of molecules are not particularly important in
understanding the phenomenon of pressure, but they are relevant to understanding why the ratio
between temperature and pressure at constant volume is different for different substances.
“Similarly, understanding how a bicycle works is best addressed by examining the structures and
their functions at the scale of, say, the frame, wheels, and pedals. However, building a lighter
bicycle may require knowledge of the properties (such as rigidity and hardness) of the materials
needed for specific parts of the bicycle. In that way, the builder can seek less dense materials with
appropriate properties; this pursuit may lead in turn to an examination of the atomic-scale structure
of candidate materials. As a result, new parts with the desired properties, possibly made of new
materials, can be designed and fabricated.” (p. 96-97)
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Progression Across the Grades
Performance Expectation from the NGSS
In grades K-2, students observe the shape and stability of
structures of natural and designed objects are related to their
function(s).
2-LS2-2. Develop a simple model that mimics the
function of an animal in dispersing seeds or
pollinating plants
In grades 3-5, students learn different materials have
different substructures, which can sometimes be observed;
and substructures have shapes and parts that serve functions.
In grades 6-8, students model complex and microscopic
structures and systems and visualize how their function
depends on the shapes, composition, and relationships among
its parts. They analyze many complex natural and designed
structures and systems to determine how they function. They
design structures to serve particular functions by taking into
account properties of different materials, and how materials
can be shaped and used.
MS-PS4-2. Develop and use a model to describe
that waves are reflected, absorbed, or transmitted
through various materials.
In grades 9-12, students investigate systems by examining
the properties of different materials, the structures of
different components, and their interconnections to reveal the
system’s function and/or solve a problem. They infer the
functions and properties of natural and designed objects and
systems from their overall structure, the way their
components are shaped and used, and the molecular
substructures of their various materials.
HS-ESS2-5. Plan and conduct an investigation of
the properties of water and its effects on Earth
materials and surface processes.
7. Stability and Change are the primary concerns of many, if not most scientific and engineering
endeavors. “Stability denotes a condition in which some aspects of a system are unchanging, at least
at the scale of observation. Stability means that a small disturbance will fade away—that is, the
system will stay in, or return to, the stable condition. Such stability can take different forms, with
the simplest being a static equilibrium, such as a ladder leaning on a wall. By contrast, a system
with steady inflows and outflows (i.e., constant conditions) is said to be in dynamic equilibrium. For
example, a dam may be at a constant level with steady quantities of water coming in and out. . . . A
repeating pattern of cyclic change—such as the moon orbiting Earth—can also be seen as a stable
situation, even though it is clearly not static.
“An understanding of dynamic equilibrium is crucial to understanding the major issues in any
complex system—for example, population dynamics in an ecosystem or the relationship between
the level of atmospheric carbon dioxide and Earth’s average temperature. Dynamic equilibrium is
an equally important concept for understanding the physical forces in matter. Stable matter is a
system of atoms in dynamic equilibrium.
“In designing systems for stable operation, the mechanisms of external controls and internal
‘feedback’ loops are important design elements; feedback is important to understanding natural
systems as well. A feedback loop is any mechanism in which a condition triggers some action that
causes a change in that same condition, such as the temperature of a room triggering the
thermostatic control that turns the room’s heater on or off.
“A system can be stable on a small time scale, but on a larger time scale it may be seen to be
changing. For example, when looking at a living organism over the course of an hour or a day, it
may maintain stability; over longer periods, the organism grows, ages, and eventually dies. For the
April 2013 NGSS Release Page 11 of 17
development of larger systems, such as the variety of living species inhabiting Earth or the
formation of a galaxy, the relevant time scales may be very long indeed; such processes occur over
millions or even billions of years.” (p. 99-100)
Progression Across the Grades
Performance Expectation from the NGSS
In grades K-2, students observe some things stay the same
while other things change, and things may change slowly or
rapidly.
2-ESS2-1. Compare multiple solutions designed to
slow or prevent wind or water from changing the
shape of the land.
In grades 3-5, students measure change in terms of
differences over time, and observe that change may occur at
different rates. Students learn some systems appear stable,
but over long periods of time they will eventually change.
In grades 6-8, students explain stability and change in
natural or designed systems by examining changes over time,
and considering forces at different scales, including the
atomic scale. Students learn changes in one part of a system
might cause large changes in another part, systems in
dynamic equilibrium are stable due to a balance of feedback
mechanisms, and stability might be disturbed by either
sudden events or gradual changes that accumulate over time
MS-LS2-4. Construct an argument supported by
empirical evidence that changes to physical or
biological components of an ecosystem affect
populations.
In grades 9-12, students understand much of science deals
with constructing explanations of how things change and
how they remain stable. They quantify and model changes in
systems over very short or very long periods of time. They
see some changes are irreversible, and negative feedback can
stabilize a system, while positive feedback can destabilize it.
They recognize systems can be designed for greater or lesser
stability.
HS-PS1-6. Refine the design of a chemical system
by specifying a change in conditions that would
produce increased amounts of products at
equilibrium.
How Are the Crosscutting Concepts Connected?
Although each of the seven crosscutting concepts can be used to help students recognize deep
connections between seemingly disparate topics, it can sometimes be helpful to think of how they
are connected to each other. The connections can be envisioned in many different ways. The
following is one way to think about their interconnections.
Patterns
Patterns stand alone because patterns are a pervasive aspect of all fields of science and
engineering. When first exploring a new phenomenon, children will notice similarities and
differences leading to ideas for how they might be classified. The existence of patterns
naturally suggests an underlying cause for the pattern. For example, observing snowflakes
are all versions of six-side symmetrical shapes suggests something about how molecules
pack together when water freezes; or, when repairing a device a technician would look for a
certain pattern of failures suggesting an underlying cause. Patterns are also helpful when
interpreting data, which may supply valuable evidence in support of an explanation or a
particular solution to a problem.
Causality
Cause and effect lies at the heart of science. Often the objective of a scientific investigation
April 2013 NGSS Release Page 12 of 17
is to find the cause that underlies a phenomenon, first identified by noticing a pattern. Later,
the development of theories allows for predictions of new patterns, which then provides
evidence in support of the theory. For example, Galileo’s observation that a ball rolling
down an incline gathers speed at a constant rate eventually led to Newton’s Second Law of
Motion, which in turn provided predictions about regular patterns of planetary motion, and a
means to guide space probes to their destinations.
Structure and function can be thought of as a special case of cause and effect. Whether the
structures in question are living tissue or molecules in the atmosphere, understanding their
structure is essential to making causal inferences. Engineers make such inferences when
examining structures in nature as inspirations for designs to meet people’s needs.
Systems
Systems and system models are used by scientists and engineers to investigate natural and
designed systems. The purpose of an investigation might be to explore how the system
functions, or what may be going wrong. Sometimes investigations are too dangerous or
expensive to try out without first experimenting with a model.
Scale, proportion, and quantity are essential considerations when deciding how to model a
phenomenon. For example, when testing a scale model of a new airplane wing in a wind
tunnel, it is essential to get the proportions right and measure accurately or the results will
not be valid. When using a computer simulation of an ecosystem, it is important to use
informed estimates of population sizes to make reasonably accurate predictions.
Mathematics is essential in both science and engineering.
Energy and matter are basic to any systems model, whether of a natural or a designed
system. Systems are described in terms of matter and energy. Often the focus of an
investigation is to determine how energy or matter flows through the system, or in the case
of engineering to modify the system, so a given energy input results in a more useful energy
output.
Stability and change are ways of describing how a system functions. Whether studying
ecosystems or engineered systems, the question is often to determine how the system is
changing over time, and which factors are causing the system to become unstable.
Conclusion
The purpose of this appendix is to explain the rationale behind integrating crosscutting concepts
into the K-12 science curriculum and to illustrate how the seven crosscutting concepts from the
Framework are integrated into the performance expectations within the NGSS. The crosscutting
concepts’ utility will be realized when curriculum developers and teachers develop lessons, units,
and courses using the crosscutting concepts to tie together the broad diversity of science and
engineering core ideas in the curriculum to realize the clear and coherent vision of the Framework.
April 2013 NGSS Release Page 13 of 17
References
AAAS (1989). Science for All Americans: a Project 2061 Report. American Association for the
Advancement of Science. Washington, D.C.: AAAS.
AAAS (1993). Benchmarks for Science Literacy, New York, NY: Oxford University Press.
NRC (1996). National science education standards. Washington DC: National Academy Press.
NSTA (2010). Science Anchors Project. http://www.nsta.org/involved/cse/scienceanchors.aspx
NRC (2012). A Framework for K-12 Science Education: Practices, Core Ideas, and Crosscutting
Concepts. Washington, DC: National Academy Press.
April 2013 NGSS Release Page 14 of 17
Performance Expectations Coded to Crosscutting Concepts
Grades K-2
Grades 3-5
Grades 6-8
Grades 9-12
Patterns
K-LS1-1, K-ESS2-1,
1-LS1-2, 1-LS3-1,
1-ESS1-1, 1-ESS1-2,
2-PS1-1, 2-ESS2-2,
2-ESS2-3
3-PS2-2, 3-LS1-1,
3-LS3-1, 3-ESS2-1,
3-ESS2-2, 4-PS4-1,
4-PS4-3, 4-ESS1-1,
4-ESS2-2, 5-ESS1-2
MS-PS1-2, MS-PS4-1, MS-
LS2-2, MS-LS4-1, MS-LS4-2,
MS-LS4-3, MS-ESS1-1, MS-
ESS2-3, MS-ESS3-2
HS-PS1-1, HS-PS1-2,
HS-PS1-3, HS-PS1-5, HS-
PS2-4, HS-LS4-1,
HS-LS4-3, HS-ESS1-5
Cause and
Effect
K-PS2-1, K-PS2-2,
K-PS3-1, K-PS3-2,
K-ESS3-2, K-ESS3-3,
1-PS4-1, 1-PS4-2,
1-PS4-3, 2-PS1-1,
2-LS2-1
3-PS2-1, 3-PS2-3,
3-LS2-1, 3-LS3-2,
3-LS4-2, 3-LS4-3,
3-ESS3-1, 4-PS4-2,
4-ESS2-1, 4-ESS3-1,
4-ESS3-2, 5-PS1-4,
5-PS2-1
MS-PS1-4, MS-PS2-3, MS-
PS2-5, MS-LS1-4, MS-LS1-5,
MS-LS2-1, MS-LS3-2, LS4-4,
MS-LS4-5, MS-LS4-6, MS-
ESS2-5, MS-ESS3-1, MS-
ESS3-3, MS-ESS3-4
HS-PS2-4, HS-PS3-5,
HS-PS4-1, HS-PS4-4,
HS-PS4-5, HS-LS2-8,
HS-LS3-1, HS-LS3-2,
HS-LS4-2, HS-LS4-4,
HS-LS4-5, HS-LS4-6,
HS-ESS2-4, HS-ESS3-1
Scale,
Proportion,
and Quantity
3-LS4-1, 5-PS1-1, 5-PS2-2,
5-PS1-3, 5-ESS1-1, 5-
ESS2-2
MS-PS1-1, MS-PS3-1, MS-
PS3-4, MS-LS1-1, MS-ESS1-
3, MS-ESS1-4, MS-ESS2-2
HS-LS2-1, HS-LS2-2,
HS-LS3-3, HS-ESS1-1, HS-
ESS1-4
Systems and
System Models
K-ESS3-1, K-ESS2-2
3-LS4-4, 4-LS1-1,
5-LS2-1 5-ESS2-1,
5-ESS3-1
MS-PS2-1, MS-PS2-4, MS-
PS3-2, MS-LS1-3, MS-ESS1-
2, MS-ESS2-6
HS-PS2-2, HS-PS3-1,
HS-PS3-4, HS-PS4-3,
HS-LS1-2, HS-LS1-4,
HS-LS2-5, HS-ESS3-6
Energy and
Matter
2-PS1-3
4-PS3-1, 4-PS3-2,
4-PS3-3, 4-PS3-4,
5-PS3-1, 5-LS1-1
MS-PS1-5, MS-PS1-6, MS-
PS3-3, MS-PS3-5, MS-LS1-6,
MS-LS1-k,
MS-LS1-7, MS-LS2-3, MS-
ESS2-4
HS-PS1-4, HS-PS1-7,
HS-PS1-8, HS-PS3-2,
HS-PS3-3, HS-LS1-5,
HS-LS1-6, HS-LS1-7,
HS-LS2-3, HS-ESS1-2, HS-
ESS1-3, HS-ESS2-3, HS-
ESS2-6
Structure and
Function
1-LS1-1, 2-LS2-2,
K-2-ETS1-2
MS-PS1-5, MS-PS1-6, MS-
PS4-a, MS-PS4-2, MS-PS4-
3, MS-LS1-6, MS-LS1-7, MS-
LS3-1
HS-PS2-6, HS-LS1-1,
HS-ESS2-5
Stability and
Change
2-ESS1-1, 2-ESS2-1
MS-PS2-2, MS-LS2-4, MS-
LS2-5, MS-ESS2-1, MS-
ESS3-5
HS-PS1-6, HS-PS4-2,
HS-LS1-3, HS-LS2-6,
HS-LS2-7, HS-ESS1-6, HS-
ESS2-1, HS-ESS2-2, HS-
ESS2-7, HS-ESS3-3, HS-
ESS3-4, HS-ESS3-5