Science Practices and Concepts


Science and Engineering Practices

Asking questions and defining problemsSEPs1: Asking Questions and Defining Problems
Asking questions and defining problems in K-12 builds on prior experiences and progresses to simple descriptive questions.

Developing and using modelsSEPs2: Developing and Using Models
Modeling in K-12 builds on prior experiences and progresses to include using and developing models (i.e., diagrams, drawing, physical replica, diorama, dramatization, or storyboard) that represent concrete events or design solutions.

Planning and carrying out investigationsSEPs3: Planning and Carrying Out Investigations
Planning and carrying out K-12 investigations to answer questions or test solutions to problems build on prior experiences and progresses to simple investigations, based on fair tests, which provide data to support explanations or design solutions.

Analyzing and interpreting dataSEPs4: Analyzing and Interpreting Data
Analyzing data in K-12 builds on prior experiences and progresses to collecting, recording, and sharing observations.

Using mathematics and computational thinkingSEPs5: Using Mathematics and Computational Thinking
Using mathematics and computational thinking in K-12 builds logical reasoning and problem-solving skills.

Constructing explanations and designing solutionsSEPs6: Constructing Explanations and Designing Solutions
Constructing explanations and designing solutions in K-12 builds on prior experiences and progresses to the use of evidence and ideas in constructing evidence-based accounts of natural phenomena and designing solutions.

Engaging in argument from evidenceSEPs7: Engaging in Argument from Evidence
Engaging in argument from evidence in K-12 builds on prior experiences and progresses to comparing ideas and representations about the natural and designed world(s).

Obtaining, evaluating, and communicating informationSEPs8: Obtaining, Evaluating, and Communicating Information
Obtaining, evaluating, and communicating information in K-12 builds on prior experiences and uses observations and texts to communicate new information.

Cross Cutting Concepts
Patterns

CCCs1: Patterns
Structures or events are often consistent and repeated.

Cause and Effect

CCCs2: Cause and Effect
Events gave causes, sometimes esimple, sometimes multifaceted.

Scale, Proportion, and Quantity

CCCs3: Scale, Proportion, and Quantity
Different measures of size and time affect a system's structure, performance, and our ability to observe phenomena.

Systems and System Models

CCCs4: Systems and System Models
A set of connected things or parts forming a complete whole.

Energy and Matter

CCCs5: Energy and Matter
Tracking energy and matter flows, into, out of, and within systems helps one understand their systems behaviors.

Structure and Function

CCCs6: Structure and Function
The ways an object is shaped or structured determines many of its properties and functions.

Stability and ChangeCCCs7: Stability and Change
Over time, a system might stay the same or become different, depending on a variety of factors.

Crosscutting Concepts

CCCs1:

Patterns

Patterns

Observed patterns in nature guide organization and classification and prompt questions about relationships and causes underlying them.

Primary (K-2) Elementary (3-5) Middle (6-8) High (9-12)
  • Patterns in the natural and human designed world can be observed, used to describe phenomena, and used as evidence.
  • Similarities and differences in patterns can be used to sort, classify, communicate and analyze simple rates of change for natural phenomena and designed products.
  • Patterns of change can be used to make predictions
  • Patterns can be used as evidence to support an explanation.
  • Macroscopic patterns are related to the nature of microscopic and atomic-level structure.
  • Graphs, charts, and images can be used to identify patterns in data.
  • Patterns in rates of change and other numerical relationships can provide information about natural systems.
  • Patterns can be used to identify cause-and-effect relationships.
  • Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena.
  • Empirical evidence is needed to identify patterns.
  • Classifications or explanations used at one scale may fail or need revision when information from smaller or larger scales is introduced; thus requiring improved investigations and experiments.
  • Patterns of performance of designed systems can be analyzed and interpreted to reengineer and improve the system.
  • Mathematical representations are needed to identify some patterns.

“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.”

While there are many patterns in nature, they are not the norm since there is a tendency for disorder 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.”

“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.”

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 Science standards.


CCCs2:

Cause and Effect

Cause and Effect

Events have causes, sometimes simple, sometimes multifaceted. Deciphering causal relationships, and the mechanisms by which they are mediated, is a major activity of science and engineering.

Primary (K-2) Elementary (3-5) Middle (6-8) High (9-12)
  • Simple tests can be designed to gather evidence to support or refute student ideas about causes.
  • Events have causes that generate observable patterns.
  • Cause and effect relationships are routinely identified, tested, and used to explain change.
  • Events that occur together with regularity might or might not be a cause and effect relationship.
  • Cause and effect relationships may be used to predict phenomena in natural or designed systems.
  • Phenomena may have more than one cause, and some cause and effect relationships in systems can only be described using probability.
  • Relationships can be classified as causal or correlational, and correlation does not necessarily imply causation.
  • Empirical evidence is required to differentiate between cause and correlation and make claims about specific causes and effects.
  • Systems can be designed to cause a desired effect.
  • Cause and effect relationships can be suggested and predicted for complex natural and human designed systems by examining what is known about smaller scale mechanisms within the system.
  • Changes in systems may have various causes that may not have equal effects.

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.”.

“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.”.

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.


CCCs3:

Scale, Proportion, and Quantity

Scale Proportion Quantity

In considering phenomena, it is critical to recognize what is relevant at different size, time, and energy scales, and to recognize proportional relationships between different quantities as scales change.

Primary (K-2) Elementary (3-5) Middle (6-8) High (9-12)
  • Relative scales allow objects and events to be compared and described (e.g., bigger and smaller; hotter and colder; faster and slower).
  • Standard units are used to measure length.
  • Natural objects and/or observable phenomena exist from the very small to the immensely large or from very short to very long time periods.
  • Standard units are used to measure and describe physical quantities such as weight, time, temperature, and volume.
  • Time, space, and energy phenomena can be observed at various scales using models to study systems that are too large or too small.
  • Proportional relationships (e.g. speed as the ratio of distance traveled to time taken) among different types of quantities provide information about the magnitude of properties and processes.
  • Phenomena that can be observed at one scale may not be observable at another scale.
  • The observed function of natural and designed systems may change with scale.
  • Scientific relationships can be represented through the use of algebraic expressions and equations.
  • The significance of a phenomenon is dependent on the scale, proportion, and quantity at which it occurs.
  • Algebraic thinking is used to examine scientific data and predict the effect of a change in one variable on another (e.g., linear growth vs. exponential growth).
  • Using the concept of orders of magnitude allows one to understand how a model at one scale relates to a model at another scale.
  • Some systems can only be studied indirectly as they are too small, too large, too fast, or too slow to observe directly.
  • Patterns observable at one scale may not be observable or exist at other scales.

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.”

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).


CCCs4:

Systems and System Models

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.

Primary (K-2) Elementary (3-5) Middle (6-8) High (9-12)
  • Systems in the natural and designed world have parts that work together.
  • Objects and organisms can be described in terms of their parts
  • A system can be described in terms of its components and their interactions.
  • A system is a group of related parts that make up a whole and can carry out functions its individual parts cannot.
  • Models can be used to represent systems and their interactions—such as inputs, processes and outputs—and energy and matter flows within systems.
  • Systems may interact with other systems; they may have sub-systems and be a part of larger complex systems.
  • Models are limited in that they only represent certain aspects of the system under study.
  • When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.
  • Models (e.g., physical, mathematical, computer models) can be used to simulate systems and interactions—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.
  • Systems can be designed to do specific tasks.

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.”

“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 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.”


CCCs5:

Energy and Matter

Energy and Matter

Tracking energy and matter flows, into, out of, and within systems helps one understand their system’s behavior.

Primary (K-2) Elementary (3-5) Middle (6-8) High (9-12)
  • Objects may break into smaller pieces and be put together into larger pieces, or change shapes.
  • Energy can be transferred in various ways and between objects. 
  • Matter is made of particles.  
  • Matter flows and cycles can be tracked in terms of the weight of the substances before and after a process occurs. The total weight of the substances does not change. This is what is meant by conservation of matter. Matter is transported into, out of, and within systems.
  • Matter is conserved because atoms are conserved in physical and chemical processes. 
  • Energy may take different forms (e.g. energy in fields, thermal energy, energy of motion). 
  • Within a natural system, the transfer of energy drives the motion and/or cycling of matter. 
  • The transfer of energy can be tracked as energy flows through a natural system.
  • In nuclear processes, atoms are not conserved, but the total number of protons plus neutrons is conserved. 
  • The total amount of energy and matter in closed systems is conserved. 
  • Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system. 
  • 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.

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 of energy output while minimizing others, in order to minimize the energy inputs needed to achieve a desired task.”


CCCs6:

Structure and Function

Structures and Functions

The way an object is shaped or structured determines many of its properties and functions.

Primary (K-2) Elementary (3-5) Middle (6-8) High (9-12)
  • The shape and stability of structures of natural and designed objects are related to their function(s).
  • Different materials have different substructures, which can sometimes be observed. 
  • Substructures have shapes and parts that serve functions.
  • Structures can be designed to serve particular functions by taking into account properties of different materials, and how materials can be shaped and used. 
  • Complex and microscopic structures and systems can be visualized, modeled, and used to describe how their function depends on the shapes, composition, and relationships among its parts, therefore complex natural structures/systems can be analyzed to determine how they function.
  • Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem. 
  • The functions and properties of natural and designed objects and systems can be inferred from their overall structure, the way their components are shaped and used, and the molecular substructures of its various materials.

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.”


CCCs7:

Stability and Change

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.

Primary (K-2) Elementary (3-5) Middle (6-8) High (9-12)
  • Things may change slowly or rapidly. 
  • Some things stay the same while other things change.
  • Change is measured in terms of differences over time and may occur at different rates. 
  • Some systems appear stable, but over long periods of time will eventually change.
  • Stability might be disturbed either by sudden events or gradual changes that accumulate over time. 
  • Explanations of stability and change in natural or designed systems can be constructed by examining the changes over time and processes at different scales, including the atomic scale. 
  • Small 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.
  • Much of science deals with constructing explanations of how things change and how they remain stable. 
  • Systems can be designed for greater or lesser stability. 
  • Feedback (negative or positive) can stabilize or destabilize a system. 
  • Change and rates of change can be quantified and modeled over very short or very long periods of time. Some system changes are irreversible.

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 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.”