College of Education, Institute for Research on Teaching
MATTER AND MOLECULES
Conveying unit purpose (Rating = , Poor)
In the Unit Introduction, Matter and Molecules describes briefly what students will learn:
For the next several weeks you will be studying matter and molecules. You will learn to explain what matter is made of and how it changes. . . .As you learn about the substances in the world around you, you will discover that this unit is different from most other science books. You will learn some new and interesting facts, but most importantly, you will use those facts to explain things in the world around you. This unit is designed to help you explain things, not just learn facts. (Science Book, p. 1s)
In describing what students will learn, Matter and Molecules uses abstractions that students are not familiar with (such as "molecules" and "substances"). In addition, the statement: "This unit is designed to help you explain things, not just learn facts" is not likely to make sense to students who have not studied units like this before that focused on developing explanations. Hence, it is not likely that this unit purpose will be comprehensible or motivating to students. Furthermore, the text merely tells students about the purpose; it does not engage them in thinking about it. The whole unit relates to the purpose identified, which is returned to at the end of the unit:
Your long study of molecules is over. We hope you have learned a lot about molecules and about how they can help you explain many different things. Can you think back to how molecules can explain the way things dissolve? What about thermal expansion? Compression of gases? Changes of state? (Science Book, p. 69s)
Conveying lesson/activity purpose (Rating = , Very Good)
Matter and Molecules routinely conveys the purpose of each activity to teachers and students in a way that would be comprehensible to students and frequently provides questions to focus students' attention on activities and to help them think about their central question before they start the activities. For example, in lesson 1.1, students engage in an activity in which they seal an ice cube in a plastic bag and try to change it into liquid water (Activity Book, activity 1.1, p. 1s). The Teacher's Guide states that the purpose of lesson 1.1 is "To help students describe ice and liquid water as two different states of the same substance" (Science Book, p. T-15). The text that students read before activity 1.1 states:
You certainly know about liquid water. That's what you drink and take showers in. But have you seen any solid water around recently? Of course you have, only you probably called it ice.
How do you know that ice is really solid water? Can you show it? You probably can, but there isn't much time, so you'll have to hurry! (Science Book, p. 2s)
The Teacher's Guide recommends that "students read the first two paragraphs of the student text. Elicit as many responses as possible to the question "How do you know that ice is really solid water?' Discuss the student responses until students understand the problem for the activity" (Science Book, p. T-15). The text that students read before to activity 1.1 asks: "How do you know that ice is really solid water? Can you show it? You probably can, but there isn't much time, so you'll have to hurry!" (Science Book, p. 2s). In introducing the activity, students are told: "You will show that ice is really solid water by changing it into liquid water, as quickly as possible" (Activity Book, p. 1s). They are encouraged to reflect on their predictions in question 2: "How does this activity show that ice and water are really the same?" (p. 1s).
The text summarizes what students have learned so far and what they need to learn or do next at appropriate points. At the beginning and the end of most lessons, there is a brief summary of what students did or learned in the previous lesson and what they will do or learn in the following lesson (e.g., see the Science Book, pp. 3-4s). In addition, at the beginning and the end of most lesson clusters, there is a brief summary of what students did or learned in the previous lesson cluster and what they will do or learn in the following lesson cluster (e.g., see the Science Book, pp. 13s, 20s).
Matter and Molecules rarely connects the purpose of individual lessons and activities to the unit purpose. An exception is the following statement at the beginning of lesson cluster 4:
In the lessons that you have already studied, you have been learning quite a bit about molecules; what they are, how small they are, how they move, how they are arranged, and so on. These lessons have been helping you explain things in terms of molecules, not just in terms of what you see, hear, or feel." (Science Book, p. 27s)
Justifying lesson/activity sequence (Rating = , Satisfactory)
Although Matter and Molecules does not give explicitly a rationale for the sequence of its activities, they appear to be connected in a logical order. Students start with simple phenomena (e.g., the melting and solidifying of ice) and move to more complex phenomena (e.g., the water cycle). In Lesson Cluster 1, the student text explains states of water in terms of the arrangement and motion of the water molecules that compose them all; in Lesson Cluster 2, the text explains differences among various liquids and solids in terms of the arrangement and motion of the molecules that compose them all; and in Lesson Cluster 3, the text explains differences among various gases in terms of their different molecular compositions. In Lesson Clusters 4 and 5, students are asked to use the ideas presented in clusters 1 through 3 to explain different phenomena (such as compressing liquids and gases and dissolving) in terms of the motion and arrangement of molecules. In cluster 6, students are asked to use the ideas in clusters 1 through 3, together with the idea that heating or cooling makes molecules move faster or slower, to explain thermal expansion. In clusters 7 through 9, students are asked to take the ideas in clusters 1 through 3, in conjunction with the ideas that heating or cooling makes molecules move faster or slower and that molecules attract each other to explain more complex phenomena: the changes of state. Matter and Molecules points out some aspects of the sequence of activities in its notes to teachers:
In Lesson Clusters 1 and 2, students learned differences among solids, liquids, and gases of substances in terms of the arrangements and motions of their molecules. The contents in Lesson Clusters 7, 8, and 9 are about how or why a substance changes from one state to another. In Lesson Cluster 6, students have learned that heating or cooling makes molecules move faster or slower. Thus, the students need to integrate scientific ideas they have already learned in understanding and explaining various changes of state in these last three lesson clusters. The specific example used is water in its three states, and the same explanation applies to other substances. (Science Book, p. T-79)
Attending to prerequisite knowledge and skills (Rating = , Satisfactory)
Matter and Molecules explicitly alerts teachers to two prerequisite ideas: in order for students to describe air in terms of its molecular composition, they must be convinced first that air is a substance, and students need to understand and become familiar with non-molecular aspects of physical changes macroscopically before they can be expected to consider theories that explain them (Science Book, p. T-5). In addition to these prerequisites, Matter and Molecules addresses other prerequisites such as: "Materials can exist in different states-solid, liquid, and gas. Some common materials, such as water, can be changed from one state to another by heating and cooling" (pp. 2-4s), and "Air is a substance that surrounds us, takes up space, and whose motion we feel as wind" (p. 22s). For example, students experiment with air in a plastic bag and attempt to fill an inverted, air-filled cup with water to help them see that air takes up space and that it is matter (hence, it is made of moving molecules). (Activity Book, pp. 12-14s)
Matter and Molecules does not provide students with experiences that can help them see that collections of pieces have properties that the individual pieces do not have. Without this prerequisite knowledge, students may attribute macroscopic phenomena (such as expansion) to the properties of individual particles (the ability to expand). Students need help in moving to the scientific view that phenomena like expansion are due to changes in the arrangement and motion of a collection of particles. For example, students could observe and describe the behavior of powders, marbles, sugar cubes, or wooden blocks (which, for example, can be "poured" out of a container) and consider that the collections may have new properties that the individual pieces do not. This is not done in Matter and Molecules, nor are students asked to think about such experiences that they might have had in earlier grades.
Alerting teacher to commonly held student ideas (Rating = , Excellent)
Matter and Molecules alerts the teacher to most of the relevant student difficulties and commonly held ideas that are documented in research studies and represents research findings in an accurate way. At the beginning of each lesson cluster, the Teacher's Guide has a chart of Conceptual Contrasts that compares the scientific view with students' misconceptions of the key ideas (see the Science Book, pp. T-14, T-27, T-40, T-48, T-61, T-69, T-80, T-90, T-100), and describes common misconceptions related to the ideas to be developed in the cluster (see the Science Book, pp. T-13, T-38, T-49, T-60, T-67-69, T-79). The contrast between the students' ideas and the scientific ideas makes it likely that teachers will understand better where the problem lies in students' ideas. For example, in the Conceptual Contrasts chart for Lesson Cluster 1, the scientific idea that "All molecules are constantly moving" is contrasted with students' conceptions that "Molecules may sometimes be still, especially in solids" and "Molecules simply share in observable movements of substances (e.g., molecules do not move in ice because ice is frozen)" (Science Book, p. T-14. These student ideas are explained further on page T-13. The Teacher's Guide also warns teachers about students' potential difficulties with the activities used to teach the key ideas. For example, when learning about liquid expansion, students put a thermometer into warm water and observe what happens to the column of colored liquid. Teachers are alerted that "Some students may think that the liquid goes up the thermometer tube when the bulb gets warmer because "heat rises'" (Science Book, p. T-74).
Assisting teacher in identifying own students' ideas (Rating = , Satisfactory)
Matter and Molecules includes some specific questions and tasks for teachers to use to find out what their students think. In some Lesson Clusters, the Activity Book contains questions to elicit students' understanding of the key ideas before they are introduced. This is made clear in the Introduction to the Activity Book:
Some questions are intended primarily for the purpose of eliciting students' ideas about topics that they have not yet studied and may only partially understand. These questions should not be graded on a right-or-wrong basis; they should be used as a basis for discussion by small groups of students or by the whole class. (p. T-i)
For example, in Activity 6.1, students place hard candy into a cup of hot water and one of cold water. They are asked to predict how what happens in the two cups will be the same, how it will be different, and to explain their predictions. This is done before students encounter the idea that molecules of hot substances move faster than those of cold substances (Activity Book, p. 31s).
In addition, teachers are supplied with two-part transparencies to encourage them to find out what their students think about the key ideas. The Science Book states that:
Each of the transparencies has two layers. The bottom layer poses a question about a situation. You should encourage students to express their ideas about that situation and the answer to the question. After your students have tried to answer the question and you are aware of how they think, you can flip down the overlay to give them a scientific answer to the question. (p. T-8)
Matter and Molecules does not make it clear whether the transparencies are to be presented before or after the scientific ideas are introduced. Hence, it is not clear whether the transparencies should be used to identify students' ideas before instruction or as tools for embedded assessment. For example, in lesson 2.3, teachers are encouraged to use Transparency 4 on page T-35 to elicit students' ideas about how molecules are arranged and how they move in solid sugar, liquid alcohol, and oxygen gas (Science Book, p. T-34). It is not clear whether this transparency is to be used before or after students learn about the different arrangement and motion of molecules in solids, liquids, and gases.
The questions that are intended to help teachers find out what students think typically ask students to make predictions or to give descriptions or explanations of properties of substances or phenomena. They are posed in ways that are likely to be comprehensible to students who are not familiar with the scientific concepts and terms. However, the text does not explicitly encourage teachers to use probing questions to clarify what students mean or to get more information about what students are thinking.
Addressing commonly held ideas (Rating = , Satisfactory)
Matter and Molecules addresses students' difficulty in appreciating the intrinsic motion of particles in solids, liquids, and gases in the Science Book (pp. T-21, T-34, T-35 [transparency]) and in the Activity Book (p. 5s, Question Set 1.3). Matter and Molecules addresses students' ideas that particles have macroscopic attributes, such as hardness, expansion, and physical state in the Science Book (pp. T-21-22, T-34-35, T-72, T-81-82) and in the Activity Book (Activity 6.2, pp. 33s, T-33; Activity 6.3, pp. 35s, T-35).
To address students' ideas, the material employs three strategies: (1) prompts students to react to commonly held misconceptions and contrast them with the scientifically correct idea (e.g., see the Activity Book, p. 33s, question 2); (2) elicits students' ideas and then juxtaposes them with the scientifically correct ideas (e.g., see the Science Book, p. T-72); or (3) suggests that teachers emphasize the correct response (e.g., see Science Book, p. T-21).
Strategy 2 may not be successful unless students are asked explicitly to contrast their ideas to the scientifically correct idea. Given the tenacity of students' misconceptions in the area of the kinetic molecular theory, it is not likely that strategy 3 (stressing the right response) will help many students to progress from their own ideas to the scientifically correct ones.
Providing a variety of phenomena (Rating = , Satisfactory)
Overall, Matter and Molecules provides several opportunities for students to have experiences with everyday phenomena relevant to the key ideas. For example, with respect to key idea c (atoms and molecules are perpetually in motion), students observe and explain the dissolution of sugar in water; the fact that left overnight, sugar spreads evenly throughout the water (rather than rises to the top or settles at the bottom); the diffusion of gases (such as perfume, ammonia, and other smells); and the tendency of gases to occupy all of the space available to them (e.g., when the valve in a scuba tank is opened, the air rushes out and one can hear it making a rushing noise). However, the unit is uneven in the number and variety of experiences that it offers to support each key idea. It provides a large number and variety of experiences for the idea that molecules are perpetually in motion, the idea that increased temperature means increased molecular motion, and changes of state. However, it gives very few experiences for the different arrangement, motion, and interaction of molecules of solids, liquids, and gases. In Matter and Molecules, several phenomena are linked to the idea that matter is made of particles; however, these phenomena illustrate how perpetually moving particles can be used to explain a variety of phenomena. The material assumes that students have accepted the idea of particles, rather than trying to make the particulate nature of matter plausible. Although the material presents the compressibility of gases and links it to molecules, the focus of the presentation is on the idea that the spaces between molecules of gases are larger than the spaces between molecules of liquids, rather than on the existence of the spaces.
Providing vivid experiences (Rating = , Excellent)
Matter and Molecules gives students an optimal number of firsthand experiences. For example, with regard to the idea that molecules are perpetually in motion, there are several hands-on experiences with phenomena that involve gases (e.g., as the release of perfume, an inflated ball) and some additional experiences with phenomena that are not hands-on (e.g., such as the examples of ammonia and lemon smells that are conveyed in pictures and text) (see the analysis of Matter and Molecules for the previous criterion: The firsthand experiences are simple and of short duration (about 15 minutes), compared to the time that students spend describing their observations and explaining them in terms of molecules (30-40 minutes). The descriptions of experiences that are not firsthand are typically sufficient to help students form a mental picture of the experience. For example, after students had the experience with the diffusion of perfume, the text talks about the diffusion of ammonia and lemon smells. Although not particularly vicarious, students are likely to form a mental picture of the experience, because they have had the perfume experience very recently and have probably had several similar experiences with smells before.
Introducing terms meaningfully (Rating = , Excellent)
Usually, Matter and Molecules presents terms in connection with a relevant experience. For example, the term "states" appears after students have had the opportunity to experience the change of state between solid and liquid water and to discuss the idea that ice and liquid water are the same substance (Science Book, p. 2s).
The technical vocabulary is restricted to the terms needed to discuss the important ideas. For example, in discussing the kinetic molecular theory, terms such as "amorphous," "crystalline solid," "cohesion," "sublimation," "viscosity," and the names of gas laws are not introduced. These terms are found frequently in middle grades science textbooks, but they are not needed to discuss the key ideas.
Representing ideas effectively (Rating = , Fair)
Matter and Molecules uses repeatedly the representation of molecules viewed through magic eyeglasses to give students a concrete picture of what the molecules might look like if they could see them. The use of magic eyeglasses may lead students to conclude that molecules are imaginary. Unfortunately, students are not asked to critique this representation or to compare it with the real thing. Drawings of molecules as seen through the magic eyeglasses represent the motion of molecules with arrows indicating the direction and motion of the molecules. Other drawings represent the different molecular arrangement and motion of molecules in the three states. Furthermore, an analogy compares the different molecular motion in the three states to students' motion in their seats, walking around the classroom and free roaming after school. (Science Book, p. T-34).
Most of the drawings-in particular, those of the arrangement and motion of molecules of solids and liquids-are not clear. This is due in part to the drawings themselves and in part to the poor printing (e.g., see Science Book, Transparency 2, p. T-30).
Generally, the representations are accurate. Unlike most other materials, Matter and Molecules typically represents the motion of molecules of solids and shows that substances are made of molecules (rather than displaying them floating in a colored background). However, some of the drawings that illustrate the relatively small size of molecules are likely to be misleading. For example, the drawing on page 7s of the Science Book shows a single cell floating in a drop of water with a border around the cell. The view through the magic eyeglasses does not make clear that the border is made of molecules.
The variety of representations for both the constant molecular motion and the different molecular arrangement and motion in solids, liquids, and gases is insufficient. Although there are some representations of these ideas, no animation or computer simulations are suggested to illustrate the different motions of solid, liquid, and gas molecules. The failure to represent dynamic processes is a deficiency.
Demonstrating use of knowledge (Rating = , Excellent)
An important goal of Matter and Molecules is "helping students use [emphasis added] scientific knowledge to develop their own personal descriptions and explanations of real-world phenomena, and thus to appreciate how interesting and useful scientific knowledge can be" (Science Book, p. T-4). Throughout Clusters 4-9, the Science Book demonstrates how knowledge about the arrangement, motion, and interaction of molecules can be used to explain everyday phenomena (pp. 28s, 32s, 35s, 36s, 41s, 42s, 44s, 48s, 54s, 57s, 60s). Most explanations provided are step-by-step (e.g., pp. 48s, 54s, 60s), are identified as demonstrations (e.g., pp. 41s, 44s, 48s, 54s, 60s), and include running commentary about important aspects of the explanation (e.g., p. 41s, 32s). This is in stark contrast to most middle school science textbooks which either never explicitly show students how to link ideas to real world phenomena or provide incomplete explanations. Both the teacher's guide and student text point to criteria for judging explanations of macroscopic phenomena that can be explained in terms of molecular arrangement and motion (e.g., Science Book, p. 32s).
Providing practice (Rating = , Very Good)
Matter and Molecules is based on the premise that an "important part of teaching science consists of giving students the chance to practice their own descriptions and explanations" of natural phenomena. Therefore, the material "includes an Activity Book containing many questions that require students to write out descriptions or explanations" (Science Book, p. T-7). As a result, throughout Matter and Molecules, students are given opportunities to practice using the key ideas to explain a variety of phenomena that one would encounter in everyday life: air pumped into a bicycle tire, the expansion of sidewalk joints, heating to loosen a jar lid, expansion of the liquid in a thermometer, etc. In addition, the Matter and Molecules Science Book recommends procedures that teachers can use to ensure that all of the students in the class get feedback. Although, overall, Matter and Molecules provides numerous tasks for students to practice their understanding of the key ideas, not enough tasks relate to the different arrangement and motion of molecules in the three states (solid, liquid, and gas). For example, only once are students asked to use the idea of the different molecular arrangement and motion in solids, liquids, and gases to explain the different properties of the three states.
Encouraging students to explain their ideas (Rating = , Excellent)
The Activity Book includes in every lesson cluster at least one set of activity sheets containing questions that prompt students to express, and sometimes justify and represent, their ideas. For example, in Lesson Cluster 4, students are asked to express their ideas on whether it would be easier to push the molecules together in a gas or in a liquid, justify their responses, and represent their thoughts about how molecules of air would be arranged in a syringe when the plunger is all the way out (Activity Book, pp. 18-19s). In addition, every lesson cluster includes a set of overhead transparencies that are designed to help teachers develop class discussions about the key ideas in the unit (Science Book, pp. T-9, T-53). The material provides opportunities for each student to state his or her views by including activity sheets on which all students are asked to record their ideas about the questions posed. The importance of giving feedback to students is stressed in the Introduction to the Science Book (p. T-6), and several mechanisms for providing feedback to students are proposed. In addition, the student book includes text that can give students feedback on their ideas about the activities. After students describe and explain phenomena using their own ideas on the activity sheets, they are frequently asked to read the text that explains the phenomena they observed (Activity Book, pp. 25-26s, Science Book, pp. 34-35s, 43s). Moreover, in contrast to curricular materials that merely state that "student answers will vary" or "provide the correct answer," the teacher notes in Matter and Molecules often include brief descriptions of likely erroneous answers, the misconceptions on which they are based, and how the teacher can respond to them.
Guiding student interpretation and reasoning (Score = , Excellent)
Matter and Molecules routinely provides question sequences to help students interpret their activities. The questions are structured carefully in order to lead students step-by-step from one insight to another (e.g., Activity Book, pp. 18-20s, 25-26s, 31-32s). Questions frame important issues, help students relate their experiences with phenomena to the scientific ideas presented, or prompt students to contrast common misconceptions with their scientific alternatives.
Encouraging students to think about what they have learned (Score = , Poor)
Matter and Molecules does not include self-monitoring as a strategy. Despite the explicitness of the introductory notes to the teacher with respect to other strategies, self-monitoring is not mentioned. In a few instances, students are asked to revise their explanations of phenomena based on what they have learned (see the Activity Book, p. 23s, question 4; Activity Book, p. 29s, question 3). But overall, Matter and Molecules does not give students opportunities to monitor their own understanding.