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About this Evaluation Report Content Analysis Instructional Analysis
| [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. |
The fifth-grade materials presume the existence of molecules and proceed as if students are familiar with this idea already. After students explore changes of state in water, the teacher is asked to “[r]eview the idea that, like all matter, water is made up of invisible particles called molecules” (5.1.1.2, LP2, p. 19, procedure 4).
(The assumption that students entering grade five will know already what molecules are and that all matter is made of molecules is not consistent with the recommendation given in Benchmarks for Science Literacy [American Association for the Advancement of Science, 1993] that students be introduced to this idea at the middle grades level.)
The idea that “all matter is composed of small building blocks called atoms” is a specific objective of grade 6, cluster 21 on building materials, their properties, and the ways in which they can be combined and shaped to withstand forces (6.3.21.1, LP1, p. 4). In contrast to the assumption made in grade five that students are familiar with atoms and molecules already, the teacher’s notes in grade six advise teachers to preassess their students’ knowledge of atomic theory and provide strategies to follow if they find that their students are not familiar with atoms and molecules yet. Following a discussion of the properties of materials, students are asked if a grain of sand can be broken down into any smaller parts (6.3.21.1, LP1, pp. 5–7). Students are reminded of a previous investigation in which they looked at different objects with a magnifying glass and were told, “You may be surprised to find out that regardless of how closely you looked, you didn't see the smallest building blocks of the materials. All of the matter on Earth is composed of small parts called atoms” (6.3.21.1, SI21–1–B, p. 3). Students are instructed to spend time accessing the glossary, which includes definitions and descriptions of the terms “atom,” “molecule,” and “matter” (6.3.21.1, LP1, p. 7). For example, the glossary includes the following description of the atom: “The smallest unit of matter that cannot be further separated or broken down by ordinary chemical means. Atoms are too small to be seen with the naked eye or by ordinary light microscopes.” Later in the sixth-grade materials, students learn about the molecules that make up food, and they are asked to explore the Some Ways in Which Heat Affects Foods Database, which contains related terms and includes again definitions and descriptions of the terms “atom,” “matter,” and “molecule” (6.4.28.1).
In the seventh-grade components, while exploring air pressure, students compare how easily water and air can be compressed. Teachers are asked to remind students that all substances are made up of “molecules” and to convey the following definition of the term “molecule” from the glossary: “The smallest part of a substance that retains all the properties of the substance and is composed of one or more atoms” (7.3.20.1, LP1, p. 3).
Finally, in the eighth-grade materials, when studying radioactivity, there is a return to the idea that all matter is made of atoms. The teacher is asked to encourage students to think about how substances—such as nails, copper wire, coins, plastic, and wooden objects—are different and how the materials they are made of are similar. The teacher is to guide the discussion to the idea that all matter is made of atoms. After this, the material goes well beyond the recommended goals for grades six through eight in Benchmarks for Science Literacy (American Association for the Advancement of Science, 1993) and National Science Education Standards (National Research Council, 1996) by discussing the components of atoms (e.g., protons and electrons), the notion of isotopes, and so forth (8.4.22.1).
Science 2000 uses the terms “atom” and “molecule” interchangeably, which may confuse students. While the fifth-grade modules use only the term “molecule,” “atom” occurs somewhat more frequently in cluster 21 of grade six. “Molecule” again predominates in the materials examined for cluster 28 of grade six and cluster 20 of grade seven. In grade eight, the emphasis shifts back again to use of the term “atom.”
Science 2000 does not attempt to contrast the atomic theory with naive theories (such as matter being continuous or just including particles), as the statement of the key idea does. On the contrary, there are several instances where the materials refer to molecules as being “in” a substance, as opposed to the substance being composed of molecules. Use of the former expression may serve to reinforce the common misconception that atoms or molecules are merely included in matter, rather than being its sole ingredient.
Idea
b: These particles are extremely small—far too small
to see directly through a microscope. One glossary entry notes that All of the matter on Earth is composed of
small parts called atoms. Atoms are so small that they can
only be seen with the most powerful microscopes in the world
something as small as the head of a pin contains more than
one billion billion atoms that’s one followed by eighteen
zeros! [sic]. [6.3.21.1, SI21–1–B, p. 3]
molecules are quite tiny. One drop of water
contains about two million quadrillion (2,000,000,000,000,000,000,000)
molecules. If we could greatly enlarge that drop of water,
making it as big as the earth, each water molecule would
only be as large as an apple or orange. [6.4.25, glossary
entry for “molecule”]
Idea
c: Atoms and molecules are perpetually in motion.
Idea
d: Increased temperature means greater molecular motion,
so most substances expand when heated.
The idea that increased temperature means greater molecular
motion is presented several times in grades five through
seven, primarily in relevant investigations and their discussion.
However, there is little that links such molecular behavior
explicitly with thermal expansion on the macroscopic scale
for any state of matter. In grade five, students observe the different rates of
diffusion of food coloring in hot and cold water and relate
their observations to molecular motion. Then, teachers are
directed to explain to the class that “as temperatures
rise (get hotter), the molecules move faster and move farther
apart from one another” (5.1.1.2, LP1, p. 20, procedure
7). In cluster 28 of grade six, lesson 1 lists as an objective:
“To learn what is happening at the molecular level
during heating” (6.4.28.1, LP1, p. 4). During an investigation
of how heating or cooking affects substances in foods, students
repeat the fifth-grade activity on the different rates of
diffusion of food coloring in hot and cold water. They observe
a video animation that is intended to represent the phase
changes of water at a molecular level and are asked what
happens to the molecules of ice and liquid water when the
molecules are heated (expected response: they “move
around more”) (6.4.28.1, SI28–1–A, pp.
1–4). The link between increased temperature and increased
molecular motion is illustrated by a set of optional investigations
and homework activities, such as how temperature affects
the solubility of gases in liquids, the dissolution of sugar
in water, the viscosity of syrup or honey, and the rate
of diffusion of tea in water (6.4.28.1, LP1). In grade seven, the idea that increased temperature means
greater molecular motion is linked to further phenomena.
For instance, students are asked to explain why a bicycle
pump gets hotter when air is pumped vigorously into a tire,
and why the circumference of a balloon changes when the
balloon is placed into water at different temperatures.
After observing the different circumferences of a balloon,
the teacher is instructed to be sure that students understand
that “[w]hen the gas molecules have greater energy,
they move faster. The faster movement means more and stronger
collisions, which increases the pressure and expands the
balloon” (7.3.20.3, LP3, p. 15). However, the link
between molecular motion and thermal expansion is not made
unequivocally at a general level for gases, and is never
presented in the context of solids or liquids.
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.
In terms of the arrangement and motion of molecules, there
are considerably more descriptions given for gases than
for liquids or solids (with there being the fewest for solids).
The spacing of molecules in the three states is the idea
addressed most frequently. In grades six through eight,
the idea appears in the glossary entries for “solids,”
“liquids,” “gases,” and the “kinetic
molecular theory.” In grade seven, students compare
the compressibility of water and air and link it to the
different spacing among molecules in the two substances
(7.3.20–1a). In grade eight, based on the different
spacing of molecules in the three states of matter, students
explain that sound travels faster in solid and liquid media
than it does in a gas medium (8.3.15.2, SI15–2). The regular arrangement of particles in solids is not mentioned
as such, with the exception of a glossary entry for “solid,”
which says that “most solids have a crystalline structure”
(8.3.15). The lack of regular arrangement of particles in
liquids, the random arrangement of gas molecules, and their
even spreading are not dealt with. The kinds of movement
of the particles in each state are addressed briefly, mostly
in the glossaries. For example, the glossary entry for “diffusion”
in grade six links the rate of diffusion to the speed at
which the molecules in a solid, liquid, or gas are moving
(6.4.27), and the entry for “gas” states that
“because gas molecules are far apart, they move about
quite freely, and the volume of the gas can be greatly compressed”
(6.3.21). Attraction among molecules is noted only briefly in passing
a few times. For instance, in grade seven, as part of the
response to a question about how liquids and gases differ,
the teacher is told (and apparently is supposed to share
with students): In a liquid, the molecules are closer together,
where they experience forces from the surrounding molecules.
These forces strongly affect the motion of the molecules.
In a gas, the molecules are farther apart and are not as
affected by the forces between molecules. [7.3.20.3, LP20,
p. 13]
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.
Molecular-level accounts of changes of state appear in
the materials for grades five, six, and seven for melting,
evaporation (boiling), and condensation. In grade five,
students observe at what temperatures water changes states
and relate their observations to molecular motion (5.1.1.2).
In grade six, students see a video entitled Phase Changes
of Water, in which there is an animation of the melting
of ice and the boiling of water, and they are asked what
happens to the molecules of ice and liquid water when heated
(6.4.28.1, SI28–1–A, pp. 1–2). In grade
seven, the regular lessons do not offer or seek molecular-level
accounts of changes of state. However, the glossary entry
for “gas” in cluster 20 of unit 3, and a video
clip that uses a popping corn analogy for molecules in each
of the three states do offer molecular-level accounts of
changes of state (7.3.20.3). Explanations of changes of
state in Science 2000 focus on the idea that as
temperatures rise, molecules move faster, move farther apart
from one another, and do not interact. For example, in grade
five, after students observe ice melting and liquid water
boiling, the teacher is directed to explain to the class
that as temperatures rise (get hotter), the molecules
move faster and move farther apart from one another. At
a certain point, they are moving so fast that they do not
form a solid mass anymore. What happens to the solid? (It
melts and turns into a liquid.) If more heat is added to
the liquid, the molecules move even farther apart. What
happens to the liquid? (It becomes a gas or vapor.) [5.1.1.2,
LP2, p. 20, procedure 7]
Given the organization of Science 2000, it is important that tasks, questions, or text be provided that tie together clearly the fairly brief and distributed experiences that students have with the key physical science ideas. Unfortunately, no such experiences are included. While the unit problem does very well at framing the activities in a unit, there does not appear to be a plan for the conceptual development of ideas across units. Key ideas are rarely related to one another; quite sophisticated ideas appear in earlier grades and are repeated in later grades. For example, the idea that increased temperature means increased molecular motion is introduced first in grade five in an activity in which food coloring diffuses at different rates in cold and hot water. Then it is used to explain melting and evaporation (5.1.1.2). The idea is addressed next in sixth-grade materials in exactly the same context (and at the same level of sophistication), with no note to students (or teachers) that they may have encountered this concept before (6.4.28.1). In grade seven, the idea is encountered in an exploration (at the molecular level) of the effects of temperature on an enclosed gas (7.3.20.3). These experiences are not linked with those that students had with this idea in the sixth-grade materials.
Not only are the different experiences that students have with an idea not tied together, but also teachers are not alerted to the individual instances in which the same idea is treated, so that they can design their own ways of connecting the experiences together. The unit overviews identify topic headings only (which are not specific enough usually to give any indication of the ideas being addressed) and rarely mention the treatment of any of the ideas in other units (at the same or earlier grades). It is interesting to note that the unit overview to grade 7, Unit 3: The Physics of Motion, the main unit in which the kinetic molecular theory is dealt with, does not even list the kinetic molecular theory as one of its topics.
Only a few explicit connections are made among the key ideas and other related ideas. Occasionally, students are asked to explain a phenomenon (such as the formation of dew), and the answer key indicates that a response at the molecular level is expected. However, it is left up to the teacher to make and explain the connection.
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 or inaccurate language is problematic in text materials, not solely 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.).
