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APPENDIX G 3. Scale, proportion, and quantity. In considering phenomena, it is critical to recognize what is relevant at different measures CROSSCUTTING CONCEPTS IN THE of size, time, and energy and to recognize how changes in NEXT GENERATION SCIENCE STANDARDS 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 Crosscutting concepts have value because they provide ideas that are applicable throughout science and engineering. students with connections and intellectual tools that are related across the differing areas of disciplinary content 5. Energy and matter: Flows, cycles, and conservation. and can enrich their application of practices and their Tracking fluxes of energy and matter into, out of, and within understanding of core ideas. (NRC, 2012, p. 233) systems helps one understand the systems’ possibilities and limitations. A Framework for K–12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (Framework) recommends science edu- 6. Structure and function. The way in which an object or liv- cation in grades K–12 be built around three major dimensions: ing thing is shaped and its substructure determine many of its science and engineering practices, crosscutting concepts that properties and functions. unify the study of science and engineering through their common 7. Stability and change. For natural and built systems alike, application across fields, and core ideas in the major disciplines conditions of stability and determinants of rates of change or of natural science. The purpose of this appendix is to describe the evolution of a system are critical elements of study. second dimension—crosscutting concepts—and to explain its role in the Next Generation Science Standards (NGSS). The Framework notes that crosscutting concepts have been fea- tured prominently for the past two decades in other documents The Framework identifies seven crosscutting concepts that bridge about what all students should learn about science. These have disciplinary boundaries, uniting core ideas throughout the fields been called “themes” in Science for All Americans (AAAS, 1989) of science and engineering. Their purpose is to help students and Benchmarks for Science Literacy (1993), “unifying prin- deepen their understanding of the disciplinary core ideas (pp. 2 ciples” in National Science Education Standards (NRC, 1996), and and 8) and develop a coherent and scientifically based view of “crosscutting ideas” the National Science Teachers Association’s the world (p. 83). The seven crosscutting concepts presented in Science Anchors Project (NSTA, 2010). Although these ideas have Chapter 4 of the Framework are as follows: been consistently included in previous standards documents, the 1. Patterns. Observed patterns of forms and events guide Framework recognizes that “students have often been expected organization and classification, and they prompt questions to build such knowledge without any explicit instructional sup- about relationships and the factors that influence them. port. Hence the purpose of highlighting them as Dimension 2 2. Cause and effect: Mechanism and explanation. Events have of the Framework is to elevate their role in the development of causes, sometimes simple, sometimes multi-faceted. A major standards, curricula, instruction, and assessments” (p. 83). The activity of science is investigating and explaining causal rela- NGSS writing team has continued this commitment by weaving tionships and the mechanisms by which they are mediated. crosscutting concepts into the performance expectations for all Such mechanisms can then be tested across given contexts and students—so they cannot be left out. used to predict and explain events in new contexts. 79

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GUIDING PRINCIPLES Repetition in different contexts will be necessary to build familiarity. Repetition is counter to the guiding principles the The Framework recommends crosscutting concepts be embedded NGSS writing team used in creating performance expectations in the science curriculum beginning in the earliest years of school- to reflect the core ideas in the science disciplines. In order to ing and suggests a number of guiding principles for how they reduce the total amount of material students are held account- should be used. The development process of the standards provides able to learn, repetition was reduced whenever possible. insights into the crosscutting concepts. These insights are shared in However, crosscutting concepts are repeated within grades at the following guiding principles. the elementary level and grade bands at the middle and high Crosscutting concepts can help students better understand core school levels so that these concepts “become common and famil- iar touchstones across the disciplines and grade levels” (p. 83). ideas in science and engineering. When students encounter new phenomena, whether in a science lab, on a field trip, or on Crosscutting concepts should grow in complexity and sophis- their own, they need mental tools to help engage in and come tication across the grades. Repetition alone is not sufficient. to understand the phenomena from a scientific point of view. As students grow in their understanding of the science disci- Familiarity with crosscutting concepts can provide that perspec- plines, depth of understanding crosscutting concepts should tive. For example, when approaching a complex phenomenon grow as well. The writing team adapted and added to the ideas (either a natural phenomenon or a machine), an approach that expressed in the Framework in developing a matrix for use in makes sense is to begin by observing and characterizing the phe- crafting performance expectations that describe student under- nomenon in terms of patterns. A next step might be to simplify standing of the crosscutting concepts. The matrix is found at the the phenomenon by thinking of it as a system and modeling its end of this section. components and how they interact. In some cases it would be Crosscutting concepts can provide a common vocabulary for useful to study how energy and matter flow through the sys- science and engineering. The practices, disciplinary core ideas, tem or how structure affects function (or malfunction). These and crosscutting concepts are the same in science and engi- preliminary studies may suggest explanations for the phenom- neering. What is different is how and why they are used—to ena, which could be checked by predicting patterns that might explain natural phenomena in science and to solve a problem emerge if the explanation is correct, and matching those predic- or accomplish a goal in engineering. Students need both types tions with those observed in the real world. of experiences to develop a deep and flexible understanding of Crosscutting concepts can help students better understand sci- how these terms are applied in each of these closely allied fields. ence and engineering practices. Because the crosscutting concepts As crosscutting concepts are encountered repeatedly across aca- address the fundamental aspects of nature, they also inform the demic disciplines, familiar vocabulary can enhance engagement way humans attempt to understand it. Different crosscutting and understanding for English language learners, students with concepts align with different practices, and when students carry language processing difficulties, and students with limited lit- out these practices, they are often addressing one of these cross- eracy development. cutting concepts. For example, when students analyze and inter- Crosscutting concepts should not be assessed separately from pret data, they are often looking for patterns in observations, practices or core ideas. Students should not be assessed on their mathematical or visual. The practice of planning and carrying out ability to define “pattern,” “system,” or any other crosscutting an investigation is often aimed at identifying cause and effect concepts as a separate vocabulary word. To capture the vision in relationships: If you poke or prod something, what will happen? the Framework, students should be assessed on the extent to The crosscutting concept of “systems and system models” is clearly which they have achieved a coherent scientific worldview by related to the practice of developing and using models. 80 NEXT GENERATION SCIENCE STANDARDS

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recognizing similarities among core ideas in science or engineer- PROGRESSION OF CROSSCUTTING CONCEPTS ing that may at first seem very different, but are united through ACROSS THE GRADES crosscutting concepts. Performance expectations focus on some but not all capabilities Following is a brief summary of how each crosscutting concept associated with a crosscutting concept. As core ideas grow in increases in complexity and sophistication across the grades as complexity and sophistication across the grades, it becomes more envisioned in the Framework. Examples of performance expecta- and more difficult to express them fully in performance expec- tions illustrate how these ideas play out in the NGSS. tations. Consequently, most performance expectations reflect 1. “Patterns exist everywhere—in regularly occurring shapes only some aspects of a crosscutting concept. These aspects are or structures and in repeating events and relationships. For indicated in the right-hand foundation box in each standard. All example, patterns are discernible in the symmetry of flowers and aspects of each core idea considered by the writing team can be snowflakes, the cycling of the seasons, and the repeated base found in the matrix at the end of this section. pairs of DNA” (p. 85). Crosscutting concepts are for all students. Crosscutting concepts While there are many patterns in nature, they are not the norm raise the bar for students who have not achieved at high levels because there is a tendency for disorder to increase (e.g., it is in academic subjects and who are often assigned to classes that far more likely for a broken glass to scatter than for scattered emphasize the “basics,” which in science may be taken to pro- bits to assemble themselves into a whole glass). In some cases, vide primarily factual information and lower-order thinking skills. order seems to emerge from chaos, as when a plant sprouts Consequently, it is essential that all students engage in using or a tornado appears amid scattered storm clouds. It is in such crosscutting concepts, which could result in leveling the playing examples that patterns exist and the beauty of nature is found. field and promoting deeper understanding for all students. “Noticing patterns is often a first step to organizing phenomena Inclusion of nature of science and engineering concepts. and asking scientific questions about why and how the patterns Sometimes included in the crosscutting concept foundation occur” (p. 85). boxes are concepts related to materials from the “Nature of “Once patterns and variations have been noted, they lead to Science” or “Science, Technology, Society, and the Environment.” questions; scientists seek explanations for observed patterns and These are not to be confused with the “Crosscutting Concepts,” for the similarity and diversity within them. Engineers often look but rather represent an organizational structure of the NGSS for and analyze patterns, too. For example, they may diagnose that recognizes concepts from both the Nature of Science and patterns of failure of a designed system under test in order to Science, Technology, Society, and the Environment that extend improve the design, or they may analyze patterns of daily and across all of the sciences. Readers should review Appendixes H seasonal use of power to design a system that can meet the fluc- and J for further information on these ideas. tuating needs” (pp. 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 organ- ism 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 Crosscutting Concepts in the Next Generation Science Standards 81

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Crosscutting Concepts: Patterns Progression Across the Grades Performance Expectation from the NGSS In grades K–2, children recognize that patterns in the natural and human designed 1-ESS1-1. Use observations of the sun, moon, and stars to describe patterns that can be world can be observed, used to describe phenomena, and used as evidence. predicted. In grades 3–5, students identify similarities and differences in order to sort and 4-PS4-1. Develop a model of waves to describe patterns in terms of amplitude and classify natural objects and designed products. They identify patterns related to wavelength and that waves can cause objects to move. time, including simple rates of change and cycles, and use these patterns to make predictions. In grades 6–8, students recognize that macroscopic patterns are related to the MS-LS4-1. Analyze and interpret data for patterns in the fossil record that document the nature of microscopic and atomic-level structure. They identify patterns in rates of existence, diversity, extinction, and change of life forms throughout the history of life on change and other numerical relationships that provide information about natural and Earth under the assumption that natural laws operate today as in the past. human designed systems. They use patterns to identify cause and effect relationships, and use graphs and charts to identify patterns in data. In grades 9–12, students observe patterns in systems at different scales and HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical cite patterns as empirical evidence for causality in supporting their explanations reaction based on the outermost electron states of atoms, trends in the periodic table, of phenomena. They recognize that classifications or explanations used at one and knowledge of the patterns of chemical properties. scale may not be useful or may 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. are identified best by using mathematical concepts. As Richard connect A and B. For example, the notion that diseases can be Feynman said, “To those who do not know mathematics it is dif- transmitted by a person’s touch was initially treated with skepti- ficult to get across a real feeling as to the beauty, the deepest cism by the medical profession for lack of a plausible mechanism. beauty, of nature. If you want to learn about nature, to appreci- Today infectious diseases are well understood as being transmit- ate nature, it is necessary to understand the language that she ted by the passing of microscopic organisms (bacteria or viruses) speaks in.” between an infected person and another. A major activity of The human brain is remarkably adept at identifying patterns, science is to uncover such causal connections, often with the and students progressively build on this innate ability through- hope that understanding the mechanisms will enable predic- out their school experiences. The following table lists the guide- tions and, in the case of infectious diseases, the design of pre- lines used by the writing team for how this progression plays out ventive measures, treatments, and cures” (p. 87). across K–12, with examples of performance expectations drawn “In engineering, the goal is to design a system to cause a desired from the NGSS. effect, so cause-and-effect relationships are as much a part of engineering as of science. Indeed, the process of design is a 2. Cause and Effect is often the next step in science, after a dis- good place to help students begin to think in terms of cause covery of patterns or events that occur together with regularity. and effect, because they must understand the underlying causal A search for the underlying cause of a phenomenon has sparked relationships in order to devise and explain a design that can some of the most compelling and productive scientific investi- achieve a specified objective” (p. 88). gations. “Any tentative answer, or ‘hypothesis,’ that A causes B requires a model or mechanism for the chain of interactions that 82 NEXT GENERATION SCIENCE STANDARDS

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Crosscutting Concepts: Cause and Effect Progression Across the Grades Performance Expectation from the NGSS In grades K–2, students learn that events have causes that generate observable 1-PS4-3. Plan and conduct an investigation to determine the effect of placing objects patterns. They design simple tests to gather evidence to support or refute their made with different materials in the path of a beam of light. own ideas about causes. In grades 3–5, students routinely identify and test causal relationships and use 4-ESS2-1. Make observations and/or measurements to provide evidence of the effects of these relationships to explain change. They understand events that occur together weathering or the rate of erosion by water, ice, wind, or vegetation. with regularity might or might not signify a cause and effect relationship. In grades 6–8, students classify relationships as causal or correlational, and MS-PS1-4. Develop a model that predicts and describes changes in particle motion, recognize that correlation does not necessarily imply causation. They use cause temperature, and state of a pure substance when thermal energy is added or removed. 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. In grades 9–12, students understand that empirical evidence is required to HS-LS3-2. Make and defend a claim based on evidence that inheritable genetic variations differentiate between cause and correlation and to make claims about specific may result from (1) new genetic combinations through meiosis, (2) viable errors occurring causes and effects. They suggest cause and effect relationships to explain and during replication, and/or (3) mutations caused by environmental factors. 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. When students perform the practice of “Planning and Carrying practice, deducing the cause of an effect is often difficult, so Out Investigations,” they often address cause and effect. At early multiple hypotheses may coexist. For example, though the occur- ages, this involves “doing” something to the system of study and rence (effect) of historical mass extinctions of organisms, such as then watching to see what happens. At later ages, experiments the dinosaurs, is well established, the reason or reasons for the are set up to test the sensitivity of the parameters involved, and extinctions (cause) are still debated, and scientists develop and this is accomplished by making a change (cause) to a single com- debate their arguments based on different forms of evidence. ponent of a system and examining, and often quantifying, the When students engage in scientific argumentation, it is often result (effect). Cause and effect is also closely associated with the centered about identifying the causes of an effect. practice of “Engaging in Argument from Evidence.” In scientific Crosscutting Concepts in the Next Generation Science Standards 83

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Crosscutting Concepts: Scale, Proportion, and Quantity 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 that natural objects and observable phenomena 5-ESS1-1. Support an argument that the apparent brightness of the sun and stars is due exist from the very small to the immensely large. They use standard units to measure to their relative distances from Earth. and describe physical quantities such as weight, time, temperature, and volume. In grades 6–8, students observe time, space, and energy phenomena at various MS-LS1-1. Conduct an investigation to provide evidence that living things are made of scales using models to study systems that are too large or too small. They cells; either one cell or many different numbers and types of cells. understand phenomena observed at one scale may not be observable at another scale and that 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. In grades 9–12, students understand that the significance of a phenomenon is HS-ESS1-4. Use mathematical or computational representations to predict the motion of dependent on the scale, proportion, and quantity at which it occurs. They recognize orbiting objects in the solar system. that patterns observable at one scale may not be observable or exist at other scales and that 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). 3. Scale, Proportion, and Quantity are important in both science how much bigger or smaller—a student must appreciate the units and engineering. These are fundamental assessments of dimension used to measure it and develop a feel for quantity” (p. 90). that form the foundation of observations about nature. Before an “The ideas of ratio and proportionality as used in science can analysis of function or process can be made (the how or why), it extend and challenge students’ mathematical understanding of is necessary to identify the what. These concepts are the starting these concepts. To appreciate the relative magnitude of some point for scientific understanding, whether it is of a total system properties or processes, it may be necessary to grasp the relation- or its individual components. Any student who has ever played the ships among different types of quantities—for example, speed as game “20 questions” understands this inherently, asking questions the ratio of distance traveled to time taken, density as a ratio of such as, “Is it bigger than a bread box?” in order to first determine mass to volume. This use of ratio is quite different than a ratio of the object’s size. numbers describing fractions of a pie. Recognition of such relation- An understanding of scale involves not only understanding that sys- ships among different quantities is a key step in forming math- tems and processes vary in size, time span, and energy, but also that ematical models that interpret scientific data” (p. 90). different mechanisms operate at different scales. In engineering, The crosscutting concept of scale, proportion, and quantity fig- “no structure could be conceived, much less constructed, without ures prominently in the practices of “Using Mathematics and the engineer’s precise sense of scale. . . . At a basic level, in order to Computational Thinking” and “Analyzing and Interpreting Data.” identify something as bigger or smaller than something else—and This concept addresses taking measurements of structures and 84 NEXT GENERATION SCIENCE STANDARDS

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Crosscutting Concepts: Systems and System Models Progression Across the Grades Performance Expectation from the NGSS In grades K–2, students understand that objects and organisms can be described K-ESS3-1. Use a model to represent the relationship between the needs of different plants in terms of their parts and that systems in the natural and designed world have or animals (including humans) and the places they live. parts that work together. In grades 3–5, students understand that a system is a group of related parts that 3-LS4-4. Make a claim about the merit of a solution to a problem caused when the make up a whole and can carry out functions its individual parts cannot. They can environment changes and the types of plants and animals that live there may change. also describe a system in terms of its components and their interactions. In grades 6–8, students understand that systems may interact with other MS-PS2-4. Construct and present arguments using evidence to support the claim that systems; they may have sub-systems and be a part of larger complex systems. gravitational interactions are attractive and depend on the masses of interacting objects. 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 also learn that models are limited in that they only represent certain aspects of the system under study. In grades 9–12, students investigate or analyze a system by defining its HS-LS2-5. Develop a model to illustrate the role of photosynthesis and cellular respiration boundaries and initial conditions, as well as its inputs and outputs. They use in the cycling of carbon among the biosphere, atmosphere, hydrosphere, and geosphere. models (e.g., physical, mathematical, computer models) to simulate the flow of energy, matter, and interactions within and between systems at different scales. They 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 also design systems to do specific tasks. phenomena, and these fundamental observations are usually and energy across it—for example, the gravitational force due to obtained, analyzed, and interpreted quantitatively. This crosscut- Earth on a book lying on a table or the carbon dioxide expelled ting concept also figures prominently in the practice of by an organism. Consideration of flows into and out of the system “Developing and Using Models.” Scale and proportion are often is a crucial element of system design. In the laboratory or even in best understood using models. For example, the relative scales of field research, the extent to which a system under study can be objects in the solar system or of the components of an atom are physically isolated or external conditions controlled is an impor- difficult to comprehend mathematically (because the numbers tant element of the design of an investigation and interpretation involved are either so large or so small), but visual or conceptual of results. . . . The properties and behavior of the whole system models make them much more understandable (e.g., if the solar can be very different from those of any of its parts, and large sys- system were the size of a penny, the Milky Way galaxy would be tems may have emergent properties, such as the shape of a tree, the size of Texas). that cannot be predicted in detail from knowledge about the components and their interactions” (p. 92). 4. Systems and System Models are useful in science and engineer- ing because the world is complex, so it is helpful to isolate a single “Models can be valuable in predicting a system’s behaviors or in system and construct a simplified model of it. “To do this, scien- diagnosing problems or failures in its functioning, regardless of tists and engineers imagine an artificial boundary between the what type of system is being examined. . . . In a simple mechani- system in question and everything else. They then examine the cal system, interactions among the parts are describable in terms system in detail while treating the effects of things outside the of forces among them that cause changes in motion or physical boundary as either forces acting on the system or flows of matter stresses. In more complex systems, it is not always possible or useful Crosscutting Concepts in the Next Generation Science Standards 85

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Crosscutting Concepts: Energy and Matter Progression Across the Grades Performance Expectation from the NGSS In grades K–2, students observe that objects may break into smaller pieces, be 2-PS1-3. Make observations to construct an evidence-based account of how an object put together into larger pieces, or change shapes. 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 that energy can be 5-LS1-1. Support an argument that plants get the materials they need for growth chiefly transferred in various ways and between objects. Students observe the conservation from air and water. of matter by tracking matter flows and cycles before and after processes and by recognizing that the total weight of substances does not change. In grades 6–8, students learn that matter is conserved because atoms are MS-ESS2-4. Develop a model to describe the cycling of water through Earth’s systems conserved in physical and chemical processes. They also learn within a natural or driven by energy from the sun and the force of gravity. 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. In grades 9–12, students learn that the total amount of energy and matter in HS-PS1-8. Develop models to illustrate changes in the composition of the nucleus of an closed systems is conserved. They can describe changes of energy and matter in a atom and the energy released during the processes of fission, fusion, and radioactive system in terms of energy and matter flows into, out of, and within that system. decay. 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. to consider interactions at this detailed mechanical level, yet it is grow. Hence, it is very informative to track the transfers of matter equally important to ask what interactions are occurring (e.g., and energy within, into, or out of any system under study. predator-prey relationships in an ecosystem) and to recognize “In many systems there also are cycles of various types. In some that they all involve transfers of energy, matter, and (in some cases, the most readily observable cycling may be of matter—for cases) information among parts of the system. . . . Any model of example, water going back and forth between Earth’s atmosphere a system incorporates assumptions and approximations; the key and its surface and subsurface reservoirs. Any such cycle of matter is to be aware of what they are and how they affect the model’s also involves associated energy transfers at each stage, so to fully reliability and precision. Predictions may be reliable but not pre- understand the water cycle, one must model not only how water cise or, worse, precise but not reliable; the degree of reliability moves between parts of the system but also the energy transfer and precision needed depends on the use to which the model mechanisms that are critical for that motion. will be put” (p. 93). “Consideration of energy and matter inputs, outputs, and flows 5. Energy and Matter are essential concepts in all disciplines of or transfers within a system or process are equally important for science and engineering, often in connection with systems. “The engineering. A major goal in design is to maximize certain types supply of energy and of each needed chemical element restricts a of energy output while minimizing others, in order to minimize system’s operation—for example, without inputs of energy (sun- the energy inputs needed to achieve a desired task” (p. 95). light) and matter (carbon dioxide and water), a plant cannot 86 NEXT GENERATION SCIENCE STANDARDS

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Crosscutting Concepts: Structure and Function Progression Across the Grades Performance Expectation from the NGSS In grades K–2, students observe that the shape and stability of structures of 2-LS2-2. Develop a simple model that mimics the function of an animal in dispersing natural and designed objects are related to their function(s). seeds or pollinating plants. In grades 3–5, students learn that 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 MS-PS4-2. Develop and use a model to describe that waves are reflected, absorbed, or and visualize how their function depends on the shapes, composition, and transmitted through various materials. 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. In grades 9–12, students investigate systems by examining the properties HS-ESS2-5. Plan and conduct an investigation of the properties of water and its effects of different materials, the structures of different components, and their on Earth materials and surface processes. interconnections to reveal a 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. 6. Structure and Function are complementary properties. “The may require knowledge of the properties (such as rigidity and shape and stability of structures of natural and designed objects hardness) of the materials needed for specific parts of the bicycle. are related to their function(s). The functioning of natural and In that way, the builder can seek less dense materials with appro- built systems alike depends on the shapes and relationships of priate properties; this pursuit may lead in turn to an examination certain key parts as well as on the properties of the materials of the atomic-scale structure of candidate materials. As a result, from which they are made. A sense of scale is necessary in order new parts with the desired properties, possibly made of new to know what properties and what aspects of shape or material materials, can be designed and fabricated” (pp. 96–97). are relevant at a particular magnitude or in investigating par- 7. Stability and Change are the primary concerns of many, if not ticular phenomena—that is, the selection of an appropriate scale most, scientific and engineering endeavors. “Stability denotes a depends on the question being asked. For example, the substruc- condition in which some aspects of a system are unchanging, at tures of molecules are not particularly important in understanding least at the scale of observation. Stability means that a small dis- the phenomenon of pressure, but they are relevant to under- turbance will fade away—that is, the system will stay in, or standing why the ratio between temperature and pressure at con- return to, the stable condition. Such stability can take different stant volume is different for different substances. forms, with the simplest being a static equilibrium, such as a lad- “Similarly, understanding how a bicycle works is best addressed by der leaning on a wall. By contrast, a system with steady inflows examining the structures and their functions at the scale of, say, and outflows (i.e., constant conditions) is said to be in dynamic the frame, wheels, and pedals. However, building a lighter bicycle equilibrium. For example, a dam may be at a constant level with Crosscutting Concepts in the Next Generation Science Standards 87

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Crosscutting Concepts: Stability and Change Progression Across the Grades Performance Expectation from the NGSS In grades K–2, students observe that some things stay the same while other 2-ESS2-1. Compare multiple solutions designed to slow or prevent wind or water from things change and that things may change slowly or rapidly. 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 that 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 MS-LS2-4. Construct an argument supported by empirical evidence that changes to systems by examining changes over time and considering forces at different scales, physical or biological components of an ecosystem affect populations. including the atomic scale. Students learn that 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. In grades 9–12, students understand that much of science deals with HS-PS1-6. Refine the design of a chemical system by specifying a change in conditions constructing explanations of how things change and how they remain stable. They that would produce increased amounts of products at equilibrium. quantify and model changes in systems over very short or very long periods of time. They see that some changes are irreversible and that negative feedback can stabilize a system, while positive feedback can destabilize it. They recognize that systems can be designed for greater or lesser stability. steady quantities of water coming in and out. . . . A repeating “A system can be stable on a small time scale, but on a larger time pattern of cyclic change—such as the moon orbiting Earth—can scale it may be seen to be changing. For example, when looking also be seen as a stable situation, even though it is clearly not at a living organism over the course of an hour or a day, it may static. maintain stability; over longer periods, the organism grows, ages, “An understanding of dynamic equilibrium is crucial to under- and eventually dies. For the development of larger systems, such as standing the major issues in any complex system—for example, the variety of living species inhabiting Earth or the formation of a population dynamics in an ecosystem or the relationship between galaxy, the relevant time scales may be very long indeed; such pro- the level of atmospheric carbon dioxide and Earth’s average tem- cesses occur over millions or even billions of years” (pp. 99–100). perature. Dynamic equilibrium is an equally important concept for understanding the physical forces in matter. Stable matter is a HOW ARE THE CROSSCUTTING CONCEPTS system of atoms in dynamic equilibrium. CONNECTED? “In designing systems for stable operation, the mechanisms of external controls and internal ‘feedback’ loops are important Although each of the seven crosscutting concepts can be used design elements; feedback is important to understanding natural to help students recognize deep connections between seemingly systems as well. A feedback loop is any mechanism in which a disparate topics, it can sometimes be helpful to think of how they condition triggers some action that causes a change in that same are connected to each other. The connections can be envisioned condition, such as the temperature of a room triggering the ther- in many different ways. The following is one way to think about mostatic control that turns the room’s heater on or off. their interconnections. 88 NEXT GENERATION SCIENCE STANDARDS

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Patterns Scale, proportion, and quantity are essential considerations when deciding how to model a phenomenon. For example, when test- Patterns stand alone because patterns are a pervasive aspect of ing a scale model of a new airplane wing in a wind tunnel, it is all fields of science and engineering. When first exploring a new essential to get the proportions right and measure accurately or phenomenon, children will notice similarities and differences the results will not be valid. When using a computer simulation of leading to ideas for how they might be classified. The existence an ecosystem, it is important to use informed estimates of popula- of patterns naturally suggests an underlying cause for the pat- tion sizes to make reasonably accurate predictions. Mathematics is tern. For example, observing that snowflakes are all versions essential in both science and engineering. of six-sided symmetrical shapes suggests something about how Energy and matter are basic to any systems model, whether of a molecules pack together when water freezes, or when repairing natural or a designed system. Systems are described in terms of a device, a technician would look for a certain pattern of failures matter and energy. Often the focus of an investigation is to deter- suggesting an underlying cause. Patterns are also helpful when mine how energy or matter flows through a system or, in the case interpreting data, which may supply valuable evidence in support of engineering, to modify a system, so that a given energy input of an explanation or a particular solution to a problem. results in a more useful energy output. Causality Stability and change are ways of describing how a system func- tions. Whether studying ecosystems or engineered systems, the Cause and effect lies at the heart of science. Often the objective question is often to determine how the system is changing over of a scientific investigation is to find the cause that underlies a time and which factors are causing the system to become unstable. phenomenon, first identified by noticing a pattern. Later, the development of a theory allows for predictions of new patterns, which then provides evidence in support of the theory. For exam- CONCLUSION ple, Galileo’s observation that a ball rolling down an incline gath- The purpose of this appendix is to explain the rationale behind ers speed at a constant rate eventually led to Newton’s Second integrating crosscutting concepts into the K–12 science curriculum Law of Motion, which in turn provided predictions about regular and to illustrate how the seven crosscutting concepts from the patterns of planetary motion and a means to guide space probes Framework are integrated into the performance expectations with- to their destinations. in the NGSS. The crosscutting concepts’ utility will be realized when Structure and function can be thought of as a special case of curriculum developers and teachers develop lessons, units, and cause and effect. Whether the structures in question are living courses using the crosscutting concepts to tie together the broad tissue or molecules in the atmosphere, understanding their struc- diversity of science and engineering core ideas in the curriculum to ture is essential to making causal inferences. Engineers make such realize the clear and coherent vision of the Framework. 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 inves- tigation 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. Crosscutting Concepts in the Next Generation Science Standards 89

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REFERENCES AAAS (American Association for the Advancement of Science). (1989). Science for all Americans. New York: Oxford University Press. AAAS. (1993). Benchmarks for science literacy. New York: Oxford University Press. Feynman, R. (1965). The Character of Physical Law. New York: Modern Library. NRC (National Research Council). (1996). National science education standards. Washington, DC: National Academy Press. NRC (2012). A framework for K–12 science education: Practices, cross- cutting concepts, and core ideas. Washington, DC: The National Academies Press. NSTA (National Science Teachers Association). (2010). Science Anchors Project. http://www.nsta.org/involved/cse/scienceanchors.aspx. 90 NEXT GENERATION SCIENCE STANDARDS

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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, 3‑PS2‑2, 3‑LS1‑1, 3‑LS3‑1, 3‑ESS2‑1, MS‑PS1‑2, MS‑PS4‑1, MS‑LS2‑2, HS‑PS1‑1, HS‑PS1‑2, HS‑PS1‑3, 1‑ESS1‑1, 1‑ESS1‑2, 2‑PS1‑1, 3‑ESS2‑2, 4‑PS4‑1, 4‑PS4‑3, MS‑LS4‑1, MS‑LS4‑2, MS‑LS4‑3, HS‑PS1‑5, HS‑PS2‑4, HS‑LS4‑1, 2‑ESS2‑2, 2‑ESS2‑3 4‑ESS1‑1, 4‑ESS2‑2, 5‑ESS1‑2 MS‑ESS1‑1, MS‑ESS2‑3, MS‑ESS3‑2 HS‑LS4‑3, HS‑ESS1‑5 Cause and Effect K‑PS2‑1, K‑PS2‑2, K‑PS3‑1, K‑PS3‑2, 3‑PS2‑1, 3‑PS2‑3, 3‑LS2‑1, 3‑LS3‑2, MS‑PS1‑4, MS‑PS2‑3, MS‑PS2‑5, HS‑PS2‑4, HS‑PS3‑5, HS‑PS4‑1, K‑ESS3‑2, K‑ESS3‑3, 1‑PS4‑1, 3‑LS4‑2, 3‑LS4‑3, 3‑ESS3‑1, 4‑PS4‑2, MS‑LS1‑4, MS‑LS1‑5, MS‑LS2‑1, HS‑PS4‑4, HS‑PS4‑5, HS‑LS2‑8, 1‑PS4‑2, 1‑PS4‑3, 2‑PS1‑1, 2‑LS2‑1 4‑ESS2‑1, 4‑ESS3‑1, 4‑ESS3‑2, MS‑LS3‑2, LS4‑4, MS‑LS4‑5, HS‑LS3‑1, HS‑LS3‑2, HS‑LS4‑2, 5‑PS1‑4, 5‑PS2‑1 MS‑LS4‑6, MS‑ESS2‑5, MS‑ESS3‑1, HS‑LS4‑4, HS‑LS4‑5, HS‑LS4‑6, MS‑ESS3‑3, MS‑ESS3‑4 HS‑ESS2‑4, HS‑ESS3‑1 Scale, Proportion, and Quantity 3‑LS4‑1, 5‑PS1‑1, 5‑PS2‑2, 5‑PS1‑3, MS‑PS1‑1, MS‑PS3‑1, MS‑PS3‑4, HS‑LS2‑1, HS‑LS2‑2, HS‑LS3‑3, 5‑ESS1‑1, 5‑ESS2‑2 MS‑LS1‑1, MS‑ESS1‑3, MS‑ESS1‑4, HS‑ESS1‑1, HS‑ESS1‑4 MS‑ESS2‑2 Systems and System Models K‑ESS3‑1, K‑ESS2‑2 3‑LS4‑4, 4‑LS1‑1, 5‑LS2‑1, 5‑ESS2‑1, MS‑PS2‑1, MS‑PS2‑4, MS‑PS3‑2, HS‑PS2‑2, HS‑PS3‑1, HS‑PS3‑4, 5‑ESS3‑1 MS‑LS1‑3, MS‑ESS1‑2, MS‑ESS2‑6 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, MS‑PS1‑5, MS‑PS1‑6, MS‑PS3‑3, HS‑PS1‑4, HS‑PS1‑7, HS‑PS1‑8, 5‑PS3‑1, 5‑LS1‑1 MS‑PS3‑5, MS‑LS1‑6, MS‑LS1‑k, HS‑PS3‑2, HS‑PS3‑3, HS‑LS1‑5, MS‑LS1‑7, MS‑LS2‑3, MS‑ESS2‑4 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, HS‑PS2‑6, HS‑LS1‑1, HS‑ESS2‑5 MS‑PS4‑2, MS‑PS4‑3, MS‑LS1‑6, MS‑LS1‑7, MS‑LS3‑1 Stability and Change 2‑ESS1‑1, 2‑ESS2‑1 MS‑PS2‑2, MS‑LS2‑4, MS‑LS2‑5, HS‑PS1‑6, HS‑PS4‑2, HS‑LS1‑3, MS‑ESS2‑1, MS‑ESS3‑5 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 Crosscutting Concepts in the Next Generation Science Standards 91

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NGSS Crosscutting Concepts* Section 2: Crosscutting Concepts Matrix K–2 Crosscutting Statements 3–5 Crosscutting Statements 6–8 Crosscutting Statements 9–12 Crosscutting Statements 1. Patterns—Observed patterns in nature guide organization and classification and prompt questions about relationships and causes underlying them. • Patterns in the natural and human • Similarities and differences in • Macroscopic patterns are related to the • Different patterns may be observed at designed world can be observed, used patterns can be used to sort, classify, nature of microscopic and atomic-level each of the scales at which a system is to describe phenomena, and used as communicate, and analyze simple rates structure. studied and can provide evidence for evidence. of change for natural phenomena and • Patterns in rates of change and other causality in explanations of phenomena. designed products. numerical relationships can provide • Classifications or explanations used at • Patterns of change can be used to make information about natural and human one scale may fail or need revision when predictions. designed systems. information from smaller or larger scales • Patterns can be used as evidence to • Patterns can be used to identify cause is introduced, thus requiring improved support an explanation. and effect relationships. investigations and experiments. • Graphs, charts, and images can be used • Patterns of performance of designed to identify patterns in data. systems can be analyzed and interpreted to reengineer and improve the system. • Mathematical representations are needed to identify some patterns. • Empirical evidence is needed to identify patterns. 2. Cause and Effect: Mechanism and Prediction—Events have causes, sometimes simple, sometimes multi-faceted. Deciphering causal relationships, and the mechanisms by which they are mediated, is a major activity of science and engineering. • Events have causes that generate • Cause and effect relationships are • Relationships can be classified as causal • Empirical evidence is required to observable patterns. routinely identified, tested, and used to or correlational, and correlation does not differentiate between cause and • Simple tests can be designed to gather explain change. necessarily imply causation. correlation and make claims about evidence to support or refute student • Events that occur together with regularity • Cause and effect relationships may be specific causes and effects. ideas about causes. might or might not be a cause and effect used to predict phenomena in natural or • Cause and effect relationships can be relationship. designed systems. suggested and predicted for complex • Phenomena may have more than one natural and human designed systems by cause, and some cause and effect examining what is known about smaller- relationships in systems can only be scale mechanisms within the system. described using probability. • Systems can be designed to cause a desired effect. • Changes in systems may have various causes that may not have equal effects. * Adapted from National Research Council. (2012). A framework for K–12 science education: Practices, crosscutting concepts, and core ideas. Washington, DC: The National Academies Press. Chapter 4: Crosscutting Concepts. 92 NEXT GENERATION SCIENCE STANDARDS

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K–2 Crosscutting Statements 3–5 Crosscutting Statements 6–8 Crosscutting Statements 9–12 Crosscutting Statements 3. Scale, Proportion, and Quantity—In considering phenomena it is critical to recognize what is relevant at different size, time, and energy scales and the proportional relationships between different quantities as scales change. • Relative scales allow objects and events • Natural objects and/or observable • Time, space, and energy phenomena • The significance of a phenomenon is to be compared and described (e.g., phenomena exist from the very small to can be observed at various scales using dependent on the scale, proportion, and bigger and smaller, hotter and colder, the immensely large or from very short to models to study systems that are too quantity at which it occurs. faster and slower). very long time periods. large or too small. • Some systems can only be studied • Standard units are used to measure • Standard units are used to measure • The observed function of natural and indirectly as they are too small, too large, length. and describe physical quantities such as designed systems may change with scale. too fast, or too slow to observe directly. weight, time, temperature, and volume. • Proportional relationships (e.g., speed • Patterns observable at one scale may not as the ratio of distance traveled to be observable or exist at other scales. time taken) among different types of • Using the concept of orders of magnitude quantities provide information about the allows one to understand how a model magnitude of properties and processes. at one scale relates to a model at another • Scientific relationships can be represented scale. through the use of algebraic expressions • Algebraic thinking is used to examine and equations. scientific data and predict the effect of a • Phenomena that can be observed at one change in one variable on another (e.g., scale may not be observable at another linear growth vs. exponential growth). scale. 4. Systems and System Models—A system is an organized group of related objects or components; models can be used for understanding and predicting the behavior of systems. • Objects and organisms can be described • A system is a group of related parts • Systems may interact with other systems; • Systems can be designed to do specific in terms of their parts. that make up a whole and can carry out they may have sub-systems and be a part tasks. • Systems in the natural and designed functions its individual parts cannot. of larger complex systems. • When investigating or describing a world have parts that work together. • A system can be described in terms of its • Models can be used to represent systems system, the boundaries and initial components and their interactions. and their interactions—such as inputs, conditions of the system need to be processes, and outputs—and energy, defined and their inputs and outputs matter, and information flows within analyzed and described using models. systems. • Models (e.g., physical, mathematical, • Models are limited in that they only computer models) can be used to represent certain aspects of the system simulate systems and interactions— under study. including energy, matter, and information flows—within and between systems at different scales. • Models can be used to predict the behavior of a system, but these predictions have limited precision and reliability due to the assumptions and approximations inherent in models. Crosscutting Concepts in the Next Generation Science Standards 93

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K–2 Crosscutting Statements 3–5 Crosscutting Statements 6–8 Crosscutting Statements 9–12 Crosscutting Statements 5. Energy and Matter: Flows, Cycles, and Conservation—Tracking energy and matter flows into, out of, and within systems helps one understand the system’s behavior. • Objects may break into smaller pieces, be • Matter is made of particles. • Matter is conserved because atoms • The total amount of energy and matter in put together into larger pieces, or change • Matter flows and cycles can be tracked are conserved in physical and chemical closed systems is conserved. shapes. in terms of the weight of the substances processes. • Changes of energy and matter in a before and after a process occurs. The • Within a natural or designed system, the system can be described in terms of total weight of the substances does transfer of energy drives the motion and/ energy and matter flows into, out of, and not change. This is what is meant or cycling of matter. within that system. by conservation of matter. Matter is • Energy may take different forms (e.g., • Energy cannot be created or destroyed— transported into, out of, and within energy in fields, thermal energy, energy of it only moves between one place and systems. motion). another place, between objects and/or • Energy can be transferred in various ways • The transfer of energy can be tracked fields, or between systems. and between objects. as energy flows through a designed or • Energy drives the cycling of matter within natural system. and between systems. • In nuclear processes, atoms are not conserved, but the total number of protons plus neutrons is conserved. 6. Structure and Function—The way an object is shaped or structured determines many of its properties and functions. • The shape and stability of structures of • Different materials have different • Complex and microscopic structures • Investigating or designing new systems or natural and designed objects are related substructures, which can sometimes be and systems can be visualized, modeled, structures requires a detailed examination to their function(s). observed. and used to describe how their function of the properties of different materials, • Substructures have shapes and parts that depends on the shapes, composition, and the structures of different components, serve functions. relationships among its parts; therefore, and connections of components to reveal complex natural and designed structures/ their function and/or solve a problem. systems can be analyzed to determine • The functions and properties of natural how they function. and designed objects and systems can be • Structures can be designed to serve inferred from their overall structure, the particular functions by taking into way their components are shaped and account properties of different materials, used, and the molecular substructures of and how materials can be shaped and their various materials. used. 94 NEXT GENERATION SCIENCE STANDARDS

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K–2 Crosscutting Statements 3–5 Crosscutting Statements 6–8 Crosscutting Statements 9–12 Crosscutting Statements 7. Stability and Change—For both designed and natural systems, conditions that affect stability and factors that control rates of change are critical elements to consider and understand. • Some things stay the same while other • Change is measured in terms of • Explanations of stability and change • Much of science deals with constructing things change. differences over time and may occur at in natural or designed systems can explanations of how things change and • Things may change slowly or rapidly. different rates. be constructed by examining changes how they remain stable. • Some systems appear stable, but over over time and forces at different scales, • Change and rates of change can be long periods of time will eventually including the atomic scale. quantified and modeled over very short change. • Small changes in one part of a system or very long periods of time. Some system might cause large changes in another changes are irreversible. part. • Feedback (negative or positive) can • Stability might be disturbed either by stabilize or destabilize a system. sudden events or gradual changes that • Systems can be designed for greater or accumulate over time. lesser stability. • Systems in dynamic equilibrium are stable due to a balance of feedback mechanisms. Crosscutting Concepts in the Next Generation Science Standards 95