AAAS Project 2061 Textbook Evaluations

## Middle Grades Science Textbooks: A Benchmarks-Based Evaluation

SciencePlus: Technology and Society. Holt, Rinehart & Winston, 1997
 Earth Science Life Science Physical Science

 [Explanation] This section examines whether the curriculum material's content aligns with the specific key ideas that have been selected for use in the analysis. [Explanation] This section examines whether the curriculum material develops an evidence-based argument in support of the key ideas, including whether the case presented is valid, comprehensible, and convincing. [Explanation] This section examines whether the curriculum material makes connections (1) among the key ideas, (2) between the key ideas and their prerequisites, and (3) between the key ideas and other, related ideas. [Explanation] This section notes whether the curriculum material presents any information that is more advanced than the set of key ideas, looking particularly at whether the “beyond literacy” information interrupts the presentation of the grade-appropriate information. [Explanation] This section notes whether the curriculum material presents any information that contains errors, misleading statements, or statements that may reinforce commonly held student misconceptions. References

Alignment

Idea a: All matter is made up of particles called atoms and molecules (as opposed to being continuous or just including particles).
There is a content match. “All matter is made up of particles” is listed as a main idea in grade six in Unit 4: Investigating Matter, Chapter 13: More about Matter, Lesson 3: A Model of Matter (Level Green, p. 237t). “All matter is composed of atoms” is cited as a main idea in grade eight in Unit 2: Particles, Chapter 5: A Case for Particles, Lesson 2: The Hidden Structure of Matter (Level Blue, p. 92t). Numerous text segments, activities, and questions related to Idea a are given in both the sixth-grade (Level Green) and eighth-grade (Level Blue) textbooks.

In grade six, students read and observe for themselves that the volume of a salt-and-water solution is smaller than the initial separate volumes of the salt and the water (Level Green, pp. 237–238st) (see Endnotes, note 1). To explain this observation, the idea is introduced that all matter is made up of particles and that there are empty spaces in between the particles (p. 238s). The text states that this idea (called the particle of matter model) is useful because it can explain many of the things that students observed previously about solids, liquids, and gases, and it asks students to use this idea to picture observations such as, “Solids and liquids cannot be compressed noticeably, but gases can be” (p. 238s). Then, students are asked to imagine that they are a particle of matter, describe what they would be doing and feeling as they went through various changes of state, and use the particle model to explain the differences between an ice cube melting in water and a sugar cube dissolving in water (p. 241st).

In grade seven, Lesson 2: Parts of a Solution—Solutes and Solvents states briefly that matter is made up of particles, uses this idea to explain the process of dissolving, and asks students to use the idea to explain why the sum of the volumes of sugar and water before mixing is greater than the volume of the solution after mixing (Level Red, p. 154s) (see Endnotes, note 2).

In grade eight, students are presented with several observations, (such as the following: ice cubes in a freezer become smaller over time (Level Blue, p. 88s); when a drop of food coloring dissolves in water, it spreads evenly throughout the solution (pp. 88–89s); sand and peas pour like water (p. 89s); and the combined volume of salt and water plus alcohol and water is less than the sum of their separate volumes (p. 90st). Students are then asked whether these observations support the idea that matter consists of particles (p. 90s).

Eighth-grade students are asked to consider the merits of three “cases” for the existence of particles and are invited to revise their own “particles case” (p. 91s). These explorations are followed by text that presents the historic development of a model for the structure of matter. It is noted that although Democritus and John Dalton were born 2,000 years apart, they both arrived at the same conclusion while thinking about the nature of matter: “Matter is made up of particles—what Democritus called atoms” (p. 92s). The simple whole number ratio of the masses of oxygen and hydrogen is described and used to infer that the particles, or atoms, of different elements have different masses (rather than being presented as evidence for the particulate nature of matter) (p. 93st). Then, it is indicated that molecules are particles that are a combination of two or more atoms and that they make up compounds (p. 95s). Next, students make further observations and expand the particle model of matter to include ideas about the motion of particles and the different arrangement of particles in solids, liquids, and gases (p. 104st). Later, the particle model is used to explain why different materials with the same volume may have different masses (p. 123st).

Unlike the statement of the key idea, SciencePlus does not contrast the atomic theory with naive theories (such as matter being continuous or just including particles). In grade eight, in the beginning of Unit 2: Particles, Chapter 5: A Case for Particles, students are asked, “If matter is made up of particles, what’s in between the particles?” (Level Blue, p. 87s). However, this question (like its accompanying misconception) is not discussed, developed, or explained at all in the student text, and is only covered later in the Annotated Teacher’s Edition (p. 106t), thereby allowing excessive time to pass for the misleading nature of the question to influence student thinking.

Idea b: These particles are extremely small—far too small to see directly through a microscope.

There is a content match. In grade eight, “Atoms and molecules are extremely small” is listed as a main idea in Unit 2: Particles, Chapter 5: A Case for Particles, Lesson 3: The Size of Particles (Level Blue, p. 99t). Some pronouncements posit that the particles that compose matter are “small,” others attempt to illustrate how extremely small particles are, and a few note that particles are too small to be seen without clarifying the statement further. In the student text points out that the particles in a solution cannot be seen even through a microscope, but it is not stated that this is true for all particles (not only those in solution) (Level Red, pp. 154–155s).

Through different kinds of activities, an effort is made to try to convey the small size of particles. However, several of these activities are misleading or are likely to be confusing to students. For example, phenomena in which solutions are formed mixing water with and other substances (such as food coloring, salt, or alcohol) are used to suggest that if matter is made up of particles, the particles of the solute (such as food coloring) are smaller than the spaces between the water particles (e.g., see Level Blue, pp. 89t, 90t). As noted previously, such a suggestion is incorrect. In the first place, most solutes are substantially larger than the spaces between water molecules. Second, the small decrease in volume observed when food coloring and water are mixed is due to the disruption in the lattice of water molecules caused by the introduction of the solute, rather than by the solute molecules fitting into the spaces between the water molecules.

The text also argues that, “If some particles are so tiny that they can pass through openings invisible to the human eye, then atoms and molecules must be extremely small” (Level Blue, p. 101s). Before this statement, there is an activity in which students detect the odor of garlic even if it is enclosed in plastic wrap (p. 100s). However, this activity does not establish definitively that the “openings” through which molecules from the garlic pass are extremely small.

Idea c: Atoms and molecules are perpetually in motion.

There is a content match. However, this idea does not receive as much explicit attention in the student text as key Ideas a and b do. In grade eight, in Unit 1: Life Processes, the student text states that particles that compose matter are in constant motion and explains how diffusion is evidence of particle motion (Level Blue, p. 37s). Also in grade eight, Unit 2: Particles, Chapter 5: A Case for Particles, Lesson 4: Particles of Solids, Liquids, and Gases lists as a prime idea that “Particles of matter are constantly in motion” (p. 103t). In this lesson, the student text adds to the particle model of matter the idea that particles move, and, to support this idea, students are expected to cite the observation that perfume diffuses (p. 104st). At the end of chapter 6, students are asked to use the idea to explain why if one traps a little smoke inside a transparent box and puts it under a microscope, one would see the particles of smoke moving in a haphazard pattern (p. 124s).

It should be noted that the eighth-grade SciencePlus SourceBook (located at the end of the student textbook) also addresses the idea that particles are in motion and links it to the diffusion in gases (perfume in the air), liquids (ink in water), and solids (if one were to stack a lead brick on top of a gold brick, a very slow diffusion would occur between these two solids) (Level Blue, pp. S30, S34). Given that the instructions in the student text imply that the SourceBook is an optional resource (for example, “If you’d like to know more about molecules and atoms, see pages S22–S26 of the SourceBook” [Level Blue, p. 96s]), information given in the SourceBook has not been taken into account in this evaluation.

Idea d: Increased temperature means greater molecular motion, so most substances expand when heated.

There is a content match. In grade eight, Unit 2: Particles, Chapter 5: A Case for Particles, Lesson 4: Particles of Solids, Liquids, and Gases specifies as a major idea that “Heating causes particles in a substance to move faster and farther apart” (Level Blue, p. 103t). In this lesson, students are to observe that food coloring diffuses faster in hot water than in cold water (pp. 103–104st); a balloon placed over the mouth of a soft-drink bottle expands when the balloon is placed in hot water and deflates when it is put in ice water (p. 104st); and alcohol evaporates faster when it is placed on a heated microscope slide than when it is placed on an unheated slide (p. 104st). Students are asked to explain these observations using the particle model of matter, and the teacher’s notes link the observations to the idea that “heated particles…move faster” (p. 104t). The student text then adds to the particle model of matter the idea that “Particles in a hot substance move faster than particles in a cold substance,” and students are expected to suggest observations that support this statement (p. 104s).

Also in grade eight, Unit 2: Particles, Chapter 6: Testing the Particle Model, Lesson 1: Temperature and Particles cites as a main idea that “As matter is heated, the motion of its particles increases, and the particles move farther apart” (Level Blue, p. 108t). Students are to observe that air, water, and glycerin in a test tube expand when the tube is placed in hot water and contract when it is placed in cold water; they are asked to draw appropriate conclusions from these observations (pp. 108–109s). The teacher’s notes link the individual observations to key Idea d; for example: “When air is heated, the molecules in the air move faster and farther apart, causing the air to expand” (p. 109t). Later, students are asked to relate how a thermometer works to the particle model of matter (p. 117s) and to explain why a certain volume of cold water would have a greater mass than the same volume of hot water (p. 123s). The student text does not link the relation between temperature and molecular motion to the thermal expansion of substances in general, as the statement of the key idea does.

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 collisions.

There is a partial content match. The following presentation of Idea e shows which parts of the idea are treated (in bold) in SciencePlus: There are differences in the arrangement and motion of atoms/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 collisions.

SciencePlus includes some activities, questions, and tasks that relate to the different arrangement and motion of particles in the three states, but very little material that relates to the interaction between particles. Comments about the different arrangement, motion, and interaction of particles in the three states appear primarily in the teacher’s notes as suggested responses to questions posed to students (either as part of the instruction or as assessment of the idea). No parts of this key idea are presented explicitly in the student text.

In the sixth grade, Unit 4: Investigating Matter, Chapter 13: More About Matter, Lesson 3: A Model of Matter, lists as a main idea that “The physical properties of solids, liquids, and gases can be explained by the particle model of matter” (Level Green, p. 237t). In this lesson, after the idea that all matter is made up of particles (Idea a) is introduced as the particle model of matter, students are asked to use the model to picture such observations as “Solids and liquids cannot be compressed noticeably, but gases can be,” “Liquids can flow, but solids are rigid,” and “Gases do not have an interface with air; solids and liquids do” (p. 238s). The suggested responses in the teacher’s notes link these observations to parts of key Idea e. For example, the suggested response to the first observation is as follows: “In solids and liquids, the particles are very close together. In gases, the particles are farther apart and can be pushed, or squeezed, closer together” (p. 238t). Next, students are asked to discuss analogies comparing solids to an audience in a stadium, liquids to basketball players on a court, and gases to a swarm of bees, then to make their own models for solids, liquids, and gases (pp. 239–240s).

In grade eight, Unit 2: Particles, Chapter 5: A Case for Particles, Lesson 4: Particles of Solids, Liquids, and Gases asserts as a prime idea that “Particles are farther apart in gases than in liquids and solids” (Level Blue, p. 103t). Students compare the compressibility of air, water, and a solid (e.g., a piece of chalk) in a syringe and are asked to add a statement to the particle model of matter on the basis of these observations. The teacher’s notes present the following as a sample answer: “Gas particles are farther apart than are the particles that make up liquids or solids” (p. 103t) (see Endnotes, note 3). At the end of the chapter, students are to create analogies to how particles of solids, liquids, and gases are moving; draw illustrations to show the behavior of particles in a solid, liquid, and gas; and write descriptions of different graphic representations of the three states of matter (pp. 105–106s). Suggested responses in the teacher’s notes focus on the different motions of particles in solids, liquids, and gases (pp. 105–106t).

It should be noted that both the sixth-grade (Level Green) and eighth-grade (Level Blue) SciencePlus SourceBooks also address parts of key Idea e. The eighth-grade book deals at some length with the forces of attraction between particles in solids, liquids, and gases, and it links differences in the arrangement, motion, and interaction of particles in solids, liquids, and gases to the properties of shape and volume (Level Blue, pp. S28–S29). However, it goes beyond the scope of this key idea in that the concepts of adhesion and surface tension are discussed (p. S28). As the student text implies that the SourceBook is an optional resource (for example, “If you’d like to know more about molecules and atoms, see pages S22–S26 of the SourceBook” [Level Blue, p. 96s]), details given the SourceBook have not been taken into account in this evaluation.

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.

There is a partial content match. The following presentation of Idea f shows which parts of the idea are treated (in bold) and what alternative vocabulary is used (in brackets) in SciencePlus: Changes of state—melting, freezing, evaporating, condensing—can be explained in terms of changes in the arrangement, interaction, and motion of [particles] atoms and molecules.

In grade six, Unit 4: Investigating Matter, Chapter 13: More About Matter, Lesson 2: Changes of State describes changes of state at a macroscopic level (Level Green, pp. 232–236st). In the same chapter, Lesson 3: A Model of Matter, after presenting the idea, “All matter is made up of particles,” asks students to think of good models for changes of state and to imagine what a particle of matter would be doing and feeling as it went through various changes of state (p. 241s). Changes of state are not explained in this lesson, so it is not clear what kinds of answers students will come up with. The teacher’s notes do not speculate about what kinds of responses to expect.

In grade eight, in Unit 2: Particles, Chapter 5: A Case for Particles, Lesson 4: Particles of Solids, Liquids, and Gases, students are to observe the condensation of water vapor from their breath on the side of a beaker filled with ice water; the evaporation and diffusion of liquid perfume throughout the classroom; and wax melting near the flame of a burning candle, then solidifying after the candle has been blown out (Level Blue, p. 104s). They are asked to explain these changes using the particle model of matter. The teacher’s notes provide brief and incomplete links of these changes to the particle model of matter primarily in terms of changes in the motion of particles, rather than in terms of changes in the arrangement, interaction, and motion of particles. For example, the suggested response to the change that involves condensation states: “Water condenses on the beaker. The beaker’s cool surface causes particles of water vapor in the breath to slow down and gather in droplets” (p. 104t). Then the student text expands the particle model of matter to include the (confusing and misleading) idea that “Liquid particles can become gas particles, and gas particles can become liquid particles,” and it asks students to suggest observations that support this statement. Subsequently, students are asked to write a story from the point of view of a particle in the solid phase as it melts and then evaporates, and to draw what happens when particles change state (p. 105t). As the student text does not include any explanations of changes of state at the molecular level, it is not clear what kinds of responses students will make. The teacher’s notes do not indicate what kinds of replies are expected from students.

It should be noted that the eighth-grade SciencePlus SourceBook contains explanations of changes of state in terms of changes in the arrangement, interaction, and motion of particles (Level Blue, p. S31). However, as the instructions in the student text imply that the SourceBook is an optional resource (for example, “If you’d like to know more about molecules and atoms, see pages S22–S26 of the SourceBook” [Level Blue, p. 96s]), information given in the SourceBook has not been included in this evaluation.

Building a Case

In grade eight, SciencePlus provides numerous activities and questions related to the particle model of matter (key ideas), even going so far as to invoke the phrases “Building the Case” (Level Blue, p. 88st) and “Testing the Particle Model” (p. 107st). Despite this encouraging focus, the material manages to build only a poorly constructed case for the particle model of matter. The following paragraphs describe the case made, examine its validity, discuss whether students are likely to understand it, and reflect on the material involving students in considering whether the argument developed supports the particle model of matter.

What is the case?
In grade eight, Unit 2: Particles, Chapter 5: A Case for Particles, Lesson 1: Building the Case begins by stating explicitly that an evidence-based argument is being made for the particulate nature of matter:

You are the judge, jury, and attorney in a landmark case—a case that will determine whether all matter is composed of particles. This case may raise as many questions about matter and its behavior as it answers. The following experiments will provide the observations and information you will need to make some important inferences as you prepare your case in favor of the particle theory of matter—or against it. [Level Blue, p. 88s]

In lesson 1, students observe several phenomena: the shrinking of ice cubes in a freezer; the dilution of a colored solution; the “pourability” of water, sand, and dried peas; and the fact that the combined volume of alcohol and water after they are mixed together is smaller than their initial separate volumes (pp. 88–90s, Exploration 1). After each observation, they are asked to think about whether the observations support the particle theory of matter; at the end, they are to summarize their case for or against the particle theory of matter, based on these observations. Then, students consider the merits of three “cases” for the existence of particles, which is followed by an invitation to revise their own “particle case” (p. 91s).

In Lesson 4: Particles of Solids, Liquids, and Gases, students are told that from circumstantial evidence, they have developed a model of the structure of matter, and that, in the following explorations, they will discover more ideas about the structure of matter to add to those they have already (p. 103s). They are then asked to perform several experiments, such as compress air, water, and a piece of solid chalk in a syringe; observe that food coloring diffuses faster in hot water than cold water; note that a balloon placed over the mouth of a soft-drink bottle expands when the balloon is placed in hot water and deflates when it is put in ice water; and see that alcohol evaporates faster when it is placed on a heated microscope slide than when it is placed on an unheated slide (pp. 103–104s, Explorations 5 and 6). After each observation, they are asked to use the particle model of matter to explain what they have observed. At the end, they are presented with an expanded list of ideas of a particle model of matter (including such ideas as, “Particles in gases are far apart,” “Particles that make up liquids and solids must be as close together as possible,” “Particles move,” and “Particles in a hot substance move faster than particles in a cold substance”) and are asked to suggest at least one observation to support each statement if they agree with it (p. 104s).

Is the case built valid?
The case made for the particle model of matter is weak. It rests on a small number of observations and involves students in drawing invalid inferences from their observations. In making the case, the material does not engage students in thinking about how the particle model compares to other explanations of the same observations or whether it can predict new observations.

The case rests largely on the ideas being supported by a few (rather than a large range of) observations: those made in Explorations 1 and 2 (for key Idea a) and those made in Explorations 5 and 6 (for key Ideas c–e). These observations are not sufficient to support an argument for the validity of the particle model of matter, so students may be left with the erroneous notions that they ought to be convinced by such limited observations and that scientists would be convinced by them. Even worse, several of the inferences that students are expected to make from these observations are not legitimate. For example, in Exploration 1, Part 3, the observation that sand pours like water is not a legitimate basis for the inference that “water is composed of particles just as sand is” (Level Blue, p. 89t). In Exploration 5, the differences in compressibility between water, air, and a piece of chalk are not a legitimate basis for the inference that “The particles of a solid are locked in place, while the particles of liquids and gases can move about” (p. 103t). (A more reasonable inference from the difference in compressibility between a liquid and a gas would be the difference in distance between their particles.) Moreover, it is unreasonable to expect students to infer the arrangement and/or motion of particles from the observation of a single instance of the macroscopic behavior of substances.

For key Idea a (as well as Ideas b–e), the text fails to encourage students to use these ideas to make empirical predictions, thus missing opportunities to establish that these particulate ideas are useful and robust. Even though chapter 6 is named “Testing the Particle Model,” it is not at all evident how the activities and text do so. The chapter focuses excessively on macroscopic renditions of heating, cooling, melting, and evaporating, with very limited discussion of these processes at the microscopic level. It is never clear that “Testing the Particle Model” is a focus of the chapter because no chance is offered for the particle model to fail. Students are merely asked to consider a few phenomena they have observed in light of the particle model of matter.

Is the case likely to be understandable?
In most of the Exploration segments, students are expected to make fairly large cognitive leaps to get from the questions posed to the answers given in the teacher text, rendering it unlikely that they will be able to make (or follow) the case for the particle model of matter. For example, in Exploration 1, Part 1, based on the observation, “In the freezer, ice cubes become smaller over time” (Level Blue, p. 88s), the following inference and possible explanation are suggested: “Perhaps ice (water) is made up of particles. Maybe some of these particles escaped from the solid state to form a gas, which floated away” (p. 89s). After students make and revise their case for or against the particle model of matter on the basis of the observations in Exploration 1, they are asked to test the strength of their case by responding to the following questions: “Does it explain why you cannot see air? Does it explain why you see sugar when it is in the sugar bowl, but not when it is dissolved in water?” (p. 91s). Students will not be able to answer these questions on the basis of the cases they have constructed, nor will they be prepared to answer them based on the experiences provided by the Exploration segments.

Does the material involve students in considering whether the argument and evidence support the particle model of matter?

Coherence

Each unit in SciencePlus begins with a table called Connecting to Other Units. This table notes connections that teachers can make between the ideas dealt with in the unit and specific ideas from other units in the same level. The Connecting to Other Units table in Unit 2: Particles (Level Blue, p. 76t) points out connections to ideas such as, “All living things are made up of particles and depend on other particles to carry out life processes” (Unit 1: Life Processes) and “Sound is propagated by particles in a medium colliding with one another” (Unit 6: Sound). The material not only notes but also (at least sometimes) makes the connection in the appropriate lesson(s). For example, with regard to the statement, “All living things are made up of particles and depend on other particles to carry out life processes,” as students learn about diffusion in Unit 1: Life Processes, they are told that diffusion is evidence of particle motion and that they will take this up in more detail in Unit 2: Particles (Level Blue, p. 37s). In Unit 2: Particles, students float an eggshell membrane on top of a solution of sugar and starch and use Benedict’s solution to detect that sugar, but not starch, passes through the membrane (p. 99s). Then, they are asked to reflect on what this indicates about the relative sizes of the two molecules and how this relates to what molecules passed through the membrane when the chick was inside (p. 100s). The Flashback! section identifies osmosis as a particular life process that depends on particles and asks students to define osmosis in terms of the particle model (p. 100s). The connection is explained more fully in the answers provided for teachers (p. 100t).

Unit 4: Investigating Matter in grade six, and Unit 2: Particles in grade eight include additional features (e.g., Theme Connections, and Integrating the Sciences) that are intended to highlight links among different science disciplines. In these features, very few relevant and appropriately placed connections are made to the key ideas.

Beyond Literacy

In introducing the particle model of matter, in grade six, Unit 4: Investigating Matter does not go beyond the key ideas. In grade eight, Unit 2: Particles contains some content that goes beyond the key ideas or is more appropriate for high school students. For example, there are descriptions of time-temperature graphs, the concepts of endothermic and exothermic change, and ideas about the structure of the atom.

Also, to illustrate how small atoms and molecules are, activities and representations based on exponents and/or very large numbers are included. For example, one figure caption states:

A single drop of water contains approximately 3 x 1021 (3,000,000,000,000,000,000,000) water molecules. If you started to count these water molecules at the rate of one per second, it would take you… Well, you do the calculation. How many minutes? How many hours? [Level Blue, p. 101s]
Suggested Response to Caption: 3 x 1021 particles ÷ 60 sec./min. x 1 sec./particle = 5 x 1019 min. 5 x 1019 min. ÷ 60 min./hr. = 833,333,333,333,333,333 hr. (or 8.3x1017hr). This is equal to 9.46 x 1013 years. (For comparison, the age of the Earth is thought to be about 4.5 x 109 years.) [p. 101t]

Given that exponents are difficult for middle school students (Benchmarks for Science Literacy [American Association for the Advancement of Science, 1993] includes this as a high school topic), it is more likely that these activities will impede rather than facilitate it learning about the small size of particles.

In most cases, material that is beyond the scope of the key ideas is separable from material that is relevant to the key ideas. For example, the structure of the atom is addressed in grade eight, in Unit 2: Particles, Chapter 7: The World of Atoms, which is located at the end of the unit and therefore could be excluded easily.

Accuracy

The evaluation teams developed a summary assessment of the most common kinds of errors found in each of the three subject areas—physical science, Earth science, and life science. In this context, “errors” is taken to mean not only outright inaccuracies, but also those instances in which the material is very likely to lead to or support student misconceptions. Overall, inducement to misconstrue is the most serious problem of accuracy in the evaluated materials.

The evaluation teams’ collective findings, presented below, should be taken as having general applicability to all of the evaluated materials, not complete and specific applicability in toto to any one of them.

Identified errors occur most frequently in drawings and other diagrams. They take the form of representations that are likely to either give rise to or reinforce misconceptions commonly held by students. Following are physical science examples of the kinds of misleading illustrative materials of most concern to the evaluation teams:

• Diagrams and drawings that show atoms or molecules of solids, liquids, and gases in colored backgrounds (for example, water molecules inside blue drop shapes) and that thereby can initiate or reinforce the misconception that particles are contained in solids, liquids, and gases, in contrast to the correct idea that substances consist of particles (with empty space between particles). This misconception may be further reinforced by the wording of diagram labels, such as “solid particles in solid water and water particles in liquid water” (emphasis added). Similarly, statements such as “explanations for what is inside things” may imply that matter contains particles (as well as other things), rather than that matter is made of particles.
• Diagrams of solids (and occasionally liquids) that do not depict the motion of atoms or molecules can give rise to, or reinforce, the misconception that atoms or molecules of solids (or liquids) are still.
• Diagrams that show molecules of liquids much farther apart than the molecules of solids are misleading; in most liquids, molecules are only a little farther apart.
• Diagrams that show particles of a substance in the solid, liquid, and gaseous state in different colors can reinforce the erroneous idea that the particles themselves are different, not their arrangement and motion. Similarly, diagrams that show particles of a substance changing size as the substance changes state can give rise to the misconception that the molecules themselves change size, becoming larger when heated.

The use of imprecise of inaccurate language is problematic in text materials, not soley in illustrations. Specifically, language that does not maintain a clear distinction between substances and atoms or molecules can mislead students to attribute macroscopic properties or behavior (such as hardness, color or physical state) to individual atoms or molecules. For example, statements such as “the particles of perfume are moving farther apart as they change into a gas and diffuse throughout the air,” “write a story from the point of view of a particle in the solid phase as it melts and then evaporates,” and “draw what happens when the particles change state” (emphasis added) imply inaccurately that the particles themselves change state (melt, evaporate, etc.).

Endnotes

1. According to the teacher’s notes, “Students may infer that the particles of salt have filled in the spaces between water particles” (p. 238t) but do not point out that this statement is incorrect. In fact, the sodium and chlorine ions do not merely fit in between the water molecules. Rather, the ions disrupt the lattice of water molecules, causing the lattice to collapse. However, this explanation requires an understanding of the lattice structure of water, which goes beyond the level of sophistication recommended for eighth-grade students in Benchmarks for Science Literacy (American Association for the Advancement of Science, 1993) and National Science Education Standards (National Research Council, 1996).

2. The suggested response in the teacher’s notes—“Because the dissolved sugar particles occupy spaces between the water molecules, the volume of the solution will be less than that of the unmixed sugar and water” (Level Red, p. 155t)—is incorrect, as pointed out above in note 1. Water is a very small molecule and most solutes are substantially larger. In the liquid state, water molecules are not spaced out nearly enough for the sugar molecules to fit in between them.

3. Before students are asked to add a statement to the particle model of matter, they are asked to conclude what differences there are between the particles of a solid and those of a liquid or a gas. The suggested response in the teacher notes—“The particles of a gas can be compressed. The particles that make up a liquid cannot be noticeably compressed. A piece of chalk could not be compressed in the syringe. The particles of a solid are locked in place, while the particles of liquids and gases can move about” (p. 103t)—is not a valid inference from these observations.