In evaluating the content of the individual middle grades science programs covered in this document, the review, or evaluation, teams have determined whether there is match between each program’s coverage of certain Earth, life, and physical science topics and a corresponding set of key ideas prepared by Project 2061. The ideas have been drawn from both Benchmarks for Science Literacy (American Association for the Advancement of Science, 1993) and National Science Education Standards (National Research Council, 1996). Each of the three idea sets has been selectively annotated to provide users with additional guidance.
Key Earth Science Ideas
This set of key ideas focuses on the changing surface of the Earth and the geologic events and processes that constantly shape and reshape it. The idea set is based on chapter 4, section C of Benchmarks and Earth and Space Science Content Standard D of National Science Education Standards.
Earth-shaping processes range from the abrupt, readily observable processes—such as volcanic eruptions and earthquakes—to the very slow, barely visible ones—such as mountain building and canyon formation. While Benchmarks postpones the treatment of plate tectonics until grades 9–12, National Science Education Standards and most state frameworks recommend that it be taught in middle school. In the absence of cognitive research related to this set of key Earth science ideas, teaching it in middle school might be feasible. Since all curriculum materials include the concept of plate tectonics by grade 8 (which is the last encounter most students have with Earth science), ideas about plate motion and the geologic events and land features that result are included in this idea set.
Idea a: The surface of the Earth is changing continually.
This idea focuses on the ever-changing nature of the surface of the Earth, as opposed to the seeing the Earth’s surface as static or unchanging. Various processes that shape and reshape the Earth’s surface—for example, erosion, plate motion, and earthquakes—can illustrate this continual change. To get credit for this idea, the curriculum material needs to refer not only to changes that have happened in the past, but also to the idea that the Earth’s surface is still changing and will likely change in the future. Descriptions of recurring events, such as earthquakes or volcanic eruptions, that do not make explicit that these processes result in the continual change of the face of the Earth, are not aligned to this key idea.
Idea b: Several processes contribute to changing the Earth’s
This idea focuses on the variety of specific factors that shape the surface of the Earth. To help students appreciate this variety, the curriculum material needs to present more than one Earth-shaping process and preferably compare a variety of processes or explicitly call students’ attention to the generalization in the idea. The emphasis should be on the effect each process has on the Earth’s surface, rather than the mechanism or other aspects of each process. For example, describing only the destructive nature of earthquakes will not constitute a match to this key idea unless the material refers to the subsequent change to the Earth’s surface. Since change is the key here, photographs, diagrams, or explanations that depict before and after scenes (for example, the effects of glaciers or waves) are credited as instances of this idea, whereas photographs of only a single time point are not. Ideally, the curriculum material should make clear that more than one process may operate simultaneously on a particular landscape (such as erosion and mountain building).
Idea c: The processes that shape the Earth today are similar
to the processes that shaped the Earth in the past.
This idea states the assumption that makes it possible to infer something about past geologic events and their relationship to current Earth features. The basis for this assumption is that the laws that govern the physical environment, such as gravity, have not changed. Ideally, the curriculum material not only states that geologists believe that the same processes that shape the Earth today have been at work in the past, but also makes reference to specific processes (such as rivers flowing downhill). The idea that Earth-shaping processes might have worked at different rates in the past goes beyond what is expected here.
Idea d: Some of the processes are abrupt, such as earthquakes
and volcanic eruptions, while some are slow, such as the movement
of continents and erosion.
This idea focuses on the time scales of various Earth-shaping processes. A complete treatment of this key idea includes both abrupt and slow changes to the surface of the Earth, as well as the explicit presentation of the generalization in the idea regarding the vast range of time frames of various processes—by means of text, discussion of the time frames of these processes, or comparison of rates. Discussion of various processes in isolation without explicit reference to the range of rates is inadequate.
Idea e: Slow but continuous processes can, over very long
times, cause significant changes on the Earth’s surface.
The focus of this idea is that slow, seemingly unnoticeable Earth-shaping processes can make significant changes to the surface of the Earth if they occur over long periods of time. Alignment to this idea requires explicit treatment of significant changes in the Earth’s surface (such as the rise of mountains or the movement of continents) that result from slow rates of change over very long time frames. Simply mentioning that some processes are slow, or that some processes have occurred over millions of years, is insufficient. To get credit for this idea, the curriculum material needs to refer to specific rates (for example, erosion of a cliff occurring at a rate of several centimeters per year), and, ideally, helps students appreciate how multiplying slow rates by long time periods can result in large changes.
Idea f: Matching coastlines and similarities in rocks and
fossils suggest that today’s continents are separated parts
of what was a single vast continent long ago.
This idea states evidence for the movement of continentals—matching coastlines, similarities in rocks, similarities in fossils—and the conclusion drawn from it—that today’s continents are separated parts of what was a single vast continent long ago. To get credit for this idea, the curriculum material does not need to address all three observations that are included specifically in this idea. However, it does need to present the idea in its historical context, that is, not only to describe the evidence but also to indicate that this is the evidence that led scientists to the idea that continents move. The material should also explain how the different pieces of evidence support the theory of continental movement, and, ideally, it should point out that continents probably moved before (and not only after) the formation of the super continent Pangaea. More recent evidence, such as magnetic data from the ocean floor, goes beyond the scope of this key idea.
Idea g: The solid crust of the Earth consists of separate
plates that move very slowly, pressing against one another in some
places, pulling apart in other places.
This idea states, in simple terms, the basic idea of plate tectonics. To get credit for this idea, the curriculum material needs to address all three aspects of the idea: (1) the solid crust of the Earth consists of separate plates; (2) these plates constantly move at a slow pace in different directions; and (3) as a result of plate motion, the plates interact with one another. While the material should make the explicit connection between plates and continents (for example, by stating that continents sit on top of the plates), the possible causes for plate motion go beyond this idea.
Idea h: Landforms and major geologic events, such as earthquakes,
volcanic eruptions, and mountain building, result from these plate
This idea links observable phenomena, such as geologic events and landforms on the Earth, to the movement of plates, stating that there is causal relationship. To get credit, the curriculum material should both explain current phenomena (for example, why Japan and the West Coast of North America are prone to earthquakes) and use the theory of plate tectonics to predict phenomena (for example, where on the Earth new mountains are likely to form).
This set of key ideas focuses on matter and energy transformations in living systems, including organisms and ecosystems. It is based on chapter 5, section E of Benchmarks and Life Science Content Standard C of National Science Education Standards.
The topic of matter and energy transformations can be treated at either the substance or molecular level in grades 6–8. At the substance level, matter transformations are seen as changing inputs into outputs—for example, carbon dioxide and water (inputs to photosynthesis) are transformed into sugars and oxygen (outputs). At the molecular level, matter transformations are seen in terms of the rearrangement of building blocks. In an evaluation, the curriculum material should first be examined to see which of the two levels it appears to emphasize and then be analyzed with that level in mind.
Idea a: Food (for example, sugars) provides molecules that
serve as fuel and building material for all organisms.
This idea is fundamental for student understanding of the other key life science ideas, especially because the everyday meaning of the term “food” is inconsistent with its biological meaning. This idea goes beyond the idea that organisms need food to grow or for energy. It can be thought of at either the substance or molecular level. At the substance level, food is the source of both the building materials that makes it possible for organisms to increase in mass and the fuel that provides the energy needed to carry out life functions (for example, add new cells, convert inputs to outputs). At the molecular level, food provides the molecular building blocks that are assembled into body structures or used as fuel. Since this idea is fundamental to the other key ideas, the level at which it is treated determines what is possible for subsequent ideas. Partial credit is given to curriculum materials that treat either the matter or the energy side of the story, but obviously, it is difficult for materials to convey the matter and energy transformations story without both parts of this idea. To receive full credit, the material needs to make the generalization (in text and concrete examples) that all organisms—not only humans—get their building materials and energy from food.
Idea b: Plants make their own food, whereas animals obtain
food by eating other organisms.
The essence of this idea is the contrast between plants, which make their own food, and animals, which do not, and hence must obtain food by eating other organisms. Alignment requires that the contrast be made explicitly.
Idea c: Matter is transformed in living systems.
The essence of this four-part idea is transformation (as opposed to just naming the reactants and products). It must be explicit that something is being transformed (that is, converted, made into, or changed) into something else.
Idea c1: Plants make sugars
from carbon dioxide (in the air) and water.
At the substance level, carbon dioxide and water are transformed into sugar (but not any of the intermediate steps). At the molecular level, the carbon, hydrogen, and oxygen atoms in carbon dioxide and water are rearranged to form sugars.
Idea c2: Plants break down
the sugars they have synthesized back into simpler substances—carbon
dioxide and water—and assemble sugars into the plants' body
structures, including some energy stores.
This idea describes the three possible fates of the sugars (sugar molecules) that plants make: (1) plants can transform some of the sugars back into carbon dioxide and water, (2) they can assemble them into body structures, or (3) they can store them for later use. The curriculum material can earn partial credit for presenting one or two of these fates, but to do so, it needs to be explicit in their treatment of transformation of matter. Observations of respiration in germinating seeds, for example, that focus on gas exchange and not on the breakdown of sugars do not align with this idea.
Idea c3: Other organisms
break down the stored sugars or the body structures of the plants
they eat (or in the animals they eat) into simpler substances and
reassemble them into their own body structures, including some energy
This idea describes the possible fates of consumed food in organisms that don’t make their own food. Food is broken down (during digestion) into sugars (and other building blocks) and the sugars can be further broken down to carbon dioxide and water; the building blocks can be reassembled into the body structures of the consumers; some of the reassembled building blocks (e.g., fat) can serve as storage forms for later use. The curriculum material can earn partial credit for presenting one or two of these ideas. To receive full credit, it should go beyond describing a single organism—such as humans—to the generalization that all consumers carry out these processes.
Idea c4: Decomposers transform
dead organisms into simpler substances, which other organisms can
This idea describes the role of decomposers in returning carbon (and nitrogen) to the environment so that they are available for use by other organisms. Complete alignment requires that the material make the notion of reuse explicit. The curriculum material should be explicit about matter transformation, although partial credit is given for statements about the “breakdown” of dead organisms.
Idea d: Energy is transformed in living systems.
The common feature of this three-part idea about energy transformations is that one form of energy is being converted into other forms—for example, light to chemical energy, chemical energy to chemical (or mechanical or electrical) energy and heat.
Idea d1: Plants use the
energy from light to make "energy-rich" sugars.
This key idea makes explicit the transformation of light energy into chemical energy (or “energy rich” sugar molecules). Curriculum materials must go beyond stating that energy is used to make sugars or to convert carbon dioxide and water into sugars (because such statements could give the impression that energy is used up in the process). At the middle school level, it is acceptable to leave vague where the energy actually is. For example, the material does not need to specify that the energy is stored in the configuration of atoms.
Idea d2: Plants get energy
by breaking down the sugars, releasing some of the energy as heat.
This idea describes the two fates in plants of the energy they store in sugars. As plants break down the sugars, they can harness some of the energy stored in sugars and they give some off as heat. Both fates are needed for a full match. The focus here is on the energy transformations; it does not matter whether matter is treated in terms of molecules or substances. However, just indicating that organisms need a source of energy to stay alive and grow is a less sophisticated idea.
Idea d3: Other organisms
get energy to grow and function by breaking down the consumed body
structures to sugars and then breaking down the sugars, releasing
some of the energy into the environment as heat.
This idea describes the two fates of the energy stored in the food consumed by other organisms. As they break down the sugars, the organisms harness some of the energy stored in sugars and they give some off as heat. Both fates are needed for a full match. The focus here is on the energy transformations; it does not matter whether matter is treated in terms of molecules or substances. However, as with Idea d2, just indicating that organisms get energy from food is a less sophisticated idea. To receive full credit, the curriculum material should go beyond describing a single organism—e.g., humans—to the generalization that all consumers carry out these processes.
Idea e: Matter and energy are transferred from one organism
to another repeatedly and between organisms and their physical environment.
This idea connects the isolated examples of matter and energy transformations in individual organisms to their repeated flow through ecosystems. The curriculum material may use the carbon cycle and/or the nitrogen cycle, but it is not necessary. A quite acceptable story could explain that as organisms consume other organisms, the food (that contains both matter and energy) is passed from the consumed organism to the consumer and is transformed in the process. Matter that leaves the bodies of organisms and returns to the environment (for example, as carbon dioxide) may be returned to living organisms through the actions of plants. However, to receive full credit, the material needs to make explicit that matter passes through food webs repeatedly—that is, over and over again.
This set of key ideas focuses on basic assumptions of the kinetic molecular theory and their use in explaining thermal expansion and changes of state. It is based on chapter 4, section D of Benchmarks and Physical Science Content Standard B of National Science Education Standards.
Idea a: All matter is made up of particles called atoms and
molecules (as opposed to being continuous or just including particles).
This idea has two aspects: (1) that matter is particulate (rather than continuous), and (2) that the particles (atoms or molecules) are the matter (rather than the commonly held incorrect idea that particles [atoms or molecules] are contained in matter). In principle, the curriculum material could teach this idea in terms of particles, without making the connection to atoms and molecules. In such cases, the content analysis part of an evaluation report should note that the material addresses this idea in terms of particles rather than in terms of atoms and molecules. If the material introduces the ideas in terms of particles and only later makes the connection to atoms and molecules, the coherence segment of the content analysis part should examine how well the material links atoms and molecules to particles. The treatment of subatomic particles goes beyond this idea.
Idea b: These particles are extremely small—far too
small to see directly through a microscope.
The idea is that atoms and molecules are far too small to see through a light microscope. Images of atoms obtained with scanning tunneling microscopes and the actual size of atoms and molecules go beyond this idea.
Idea c: Atoms and molecules are perpetually in motion.
The idea is that atoms and molecules of all matter are perpetually in motion. A complete content match to this idea would make clear that molecules of solids, liquids, and gases are in motion.
Idea d: Increased temperature means greater molecular motion,
so most substances expand when heated.
This idea has three components: (1) the relationship between temperature and molecular motion; (2) thermal expansion of solids, liquids, and gases; and (3) the connection between changes in the motion of molecules (with increased temperature) and thermal expansion. The link between increased temperature and average energy of motion of molecules (a more sophisticated idea) does not serve as a basis for this analysis. The curriculum material should neither be held accountable for presenting the link between increased temperature and average energy of motion, nor penalized for including it.
Idea e: There are differences in the arrangement and motion
of atoms and molecules in solids, liquids, and gases. In solids, particles
(1) are packed closely, (2) are (often) arranged regularly, (3) vibrate
in all directions, (4) attract and “stick to” one another.
In liquids, particles (1) are packed closely, (2) are not arranged
regularly, (3) can slide past one another, (4) attract and are connected
loosely to one another. In gases, particles (1) are far apart, (2)
are arranged randomly, (3) spread evenly through the spaces they occupy,
(4) move in all directions, (5) are free of one another, except during
This idea focuses on the differences in proximity, arrangement, motion, and interaction of atoms and molecules of solids, liquids, and gases. The nature of interactions between and within molecules (for example, types of bonds) goes beyond this idea.
Idea f: Changes of state—melting, freezing, evaporating,
condensing—can be explained in terms of changes in the arrangement,
interaction, and motion of atoms and molecules.
This idea focuses on the molecular explanation of changes of state. Descriptions of changes of state only in terms of heat transfer are not sufficient for alignment. Descriptions of phase diagrams go beyond this idea.