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Middle Grades Science Textbooks: A Benchmarks-Based Evaluation

BSCS Middle School Science & Technology: Patterns of Change, Level A. Kendall/Hunt Publishing Company, 1999
Earth Science Life Science Physical Science

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.


Idea a: The surface of the Earth is changing continually.
There is not a content match. Although the student text discusses Earth-changing processes, the emphasis is on recurring processes rather than on a continually changing surface of the Earth:
[T]he processes that formed the earth are still taking place today. Volcanoes are still erupting, and they have erupted many times before. They are an example of molten rock breaking through the surface. This molten rock has cooled and has formed the hard surface of the earth. This process is still going on. [p. 180s]

The introduction to Unit 2: Explanation for the Patterns of Change on Earth and Beyond briefly mentions that patterns in the layers of the Earth explain how the Earth has changed over time (p. 137s), but the unit's chapters provide no evidence of a changing Earth's surface. Overall, the explanations, diagrams, and questions provided do not focus on how these processes continually change the surface of the Earth (e.g., pp. 187-191, 214-218s). More importantly, no part of the student text or Teacher's Edition provides a contrast to the commonly held student idea that the surface of the Earth is static and unchanging.

The Teacher's Edition shows the changes in the locations of the continents over time (pp. 220-221t) but does not explain that the surface of the Earth is continually changed by the motion of continents. In another instance, it mentions that earthquakes have occurred throughout human history (157a-157ct), but does not mention how earthquakes have changed the Earth's surface.

Idea b: Several processes contribute to changing the Earth’s surface.
There is a content match. The text describes processes of mountain formation, including folding and faulting (pp. 214-215s), and a question asks, "[H]ow does the landscape change after a severe earthquake?" (p. 213s). Unfortunately, other Earth-shaping processes such as weathering, erosion, and deposition, are not mentioned. The Teacher's Edition provides information about how volcanoes can lead to mountain formation-information that is to be presented in a class discussion or assigned as an additional reading:

Mauna Loa is the world's largest volcano and the largest single mountain in terms of volume. It rises nearly 4200 meters above sea level and fully 9000 meters above the seafloor. It is approximately 100 kilometers in diameter, with a circumference approaching 320 kilometers. All this immense bulk has been built up by intermittent lava flows over many thousands of years. [p. 157ct]

Although the student text presents a few geological events (e.g., faults [p. 215s] and volcanoes [pp. 216-217s]), it does not focus on the changes made to the surface of the Earth.

Idea c: The processes that shape the Earth today are similar to the processes that shaped the Earth in the past.
There is a content match. This idea is stated once in the Teacher's Edition (p. 163t) and once in the student text (p. 180s). In the student play, the character James Hutton says, "[T]he processes that formed the earth are still taking place today" and gives the example of volcanoes (p. 180s). But this idea is not further developed, nor is it linked to other geological events. Furthermore, the play also contains several antiquated ideas about the causes of earthquakes and volcanoes (e.g., pp. 164s, 167-168s, 169s), but does not help the students distinguish which ideas are scientifically sound and which are not. Students might not be able to discern that Hutton's idea is still accepted today while Strabo's idea (that wind pushes ash and rocks into the air as volcanoes erupt) is not.

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.
There is a content match. The introduction to Chapter 9: Volcanoes, Earthquakes, and Explanations asks students to think about the fact that earthquakes and volcanoes can be sudden events (p. 157s). Although the student text mentions briefly that some processes can be sudden, these two sudden events are not contrasted with slower or more subtle geological events. Later, students read that North and South America are moving away from Africa at a very slow rate, (p. 198s), and diagrams of the Earth show the past locations of continents (pp. 220-221s). However, none of these sightings mentions how the rate of the event is related to the change on the surface of the Earth.

The Teacher's Edition also provides information about abrupt and slow processes that could be used in class discussions or as supplemental readings.  The chapter 9  Background Information feature explains that earthquakes occur without warning, that the building of a volcano in Mexico occurred over months, and that the islands of Hawaii have been built over many thousands of years (pp. 157a-157ct).

Idea e: Slow but continuous processes can, over very long times, cause significant changes on the Earth’s surface.
There is a content match. The Teacher's Edition suggests that teachers present and illustrate this key idea when introducing an activity on moving continents:

Introduce Part A of the investigation as follows. Point out that the procedure tells them that North America and South America are moving away from Africa and Europe at a rate of about 2.5 centimeters per year. Point out this distance on a metric ruler. Help them grasp the implications of this. It might not seem like much in the short term-this is about half as fast as a fingernail grows. In the last 10 years these continents have moved apart by 25 centimeters. Although this is not very far, it translates into large distances over long periods of time; 250 centimeters (8 feet) in 100 years, 24 meters (80 feet) in 1,000 years, about 1 kilometer (0.6 miles) in 10,000 years, 10 kilometers (6.2 miles) in 1 million years, and about 2,000 kilometers (3226 miles-more than a third of the distance across the United States) in 200 million years, if we assume a constant rate of movement. [p. 198t]

(Unfortunately the preceding passage is marred by obvious arithmetic errors.) Later, the student text shows the positions of continents at various points on a geologic timeline (pp. 220-221s). However, the accompanying text does not explain how the slow change over long times can cause a significant change to the surface of the Earth. This idea is not mentioned in any other context, such as the wearing down of mountains or building up of sediment.

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.
There is a content match. The student text presents the idea in the context of describing Wegener's theory of continental drift:

Wegener thought that because the shapes of continents fit together like a puzzle, it was likely that the continents had been together at one time and later moved to their present location.. [G]eologists found fossils in Africa and Australia that were similar to fossils in South America and Antarctica.... This evidence suggested that the continents had been together but then moved apart. [pp. 199-200s]

Diagrams of Pangaea and the fossil evidence (that similar fossils found on now far spread continents) are included in Blackline Masters (Teacher's Resources Book, Assessment Tools, BLM 10.3, BLM 10.4).

Idea g: The solid crust of the Earth consists of separate plates that move very slowly, pressing against and sliding past one another in some places, pulling apart in other places.
There is a content match. This idea is described in both the Teacher's Edition (pp. 195-196t) and the student text. Students read that "continents sit on top of plates that make up the entire surface of the Earth. It is these plates that move.. [A]s the plates rub against each other, they cause earthquakes. Volcanoes occur where plates move apart or where one plate pushes and melts beneath another plate" (pp. 201-202s). A map in the student text shows the Earth's major plates and how they are interacting (that is, pushing together, pulling apart, or moving side by side) (p. 202s).

Idea h: Landforms and major geologic events, such as earthquakes, volcanic eruptions, and mountain building, result from these plate motions.
There is a content match. The student text explains and illustrates how volcanoes, earthquakes, ridges and trenches are related to plate boundaries (pp. 201-211s). Furthermore, the Teacher's Edition encourages teachers to introduce the reading by having students "compare the diagram of plate boundaries in their book (Figure 10.2) with the locations of earthquakes and volcanoes shown in Chapter 9" (p. 200t).

Building a Case

Patterns of Change attempts to build a case for the theory of plate tectonics by presenting the evidence and conclusions as they were arrived at historically. However, the attempt to develop the theory by unfolding the evidence may be quite difficult for sixth-grade students to comprehend. Hence students may be left with little understanding of both the key Earth science ideas and ideas about how science works.

Chapter 9 presents evidence for the theory of plate tectonics. Students examine maps of the ocean floor, the locations of volcanoes, the locations of earthquakes, and the ages of rocks (pp. 186-189s). Accompanying questions encourage students to find patterns in these data, but they are not helped to link the data to the theory of underlying moving plates at this time. In chapter 10, students observe that existing continents can be fitted together like pieces of a puzzle (pp. 197-199s), and they read about Wegener's newsprint analogy and additional evidence from fossils and the locations of earthquakes and volcanoes that led scientists to conclude that continents have moved (pp. 199-201s). Although the text presents some of the evidence-such as the existence of similar fossils on widely separated coasts-it fails to point out that it is very unlikely for organisms to develop in exactly the same way in separate environments. Without this argument, the fossil evidence may not be convincing. And when the text finally presents the theory of plate tectonics, it only briefly relates it to the evidence:

Geologists concluded that the surface of the earth is moving, but it is not just the continents that are moving. Geologists continued to explain that the continents sit on top of plates that make up the entire surface of the earth. It is these plates that move (see Figure 10.2). We call this explanation the theory of plate tectonics. According to this explanation, as the plates rub against each other, they cause earthquakes. Volcanoes occur where the plates move apart or where one plate pushes and melts beneath another plate. This also explains why the rocks are youngest in the middle of the Atlantic Ocean. Along the Mid-Atlantic Ridge, two plates are pulling apart and new lava is rising up between them. As this lava cools, it forms the youngest rocks. [pp. 201-202s]

Students are expected to relate the evidence to the theory in responding to Stop and Think questions:

1.       List some of the patterns that scientists noticed but did not know how to explain. [Answer: Geologists noticed patterns in the shapes of continents and the locations of fossils, volcanoes, and earthquakes.]

2.       How does the theory of plate tectonics explain earthquakes? [Answer: Earthquakes are the result of two plates rubbing against each other or the result of one plate moving beneath the other.]

3.       According to the theory of plate tectonics, why are the youngest rocks in the Atlantic Ocean in the middle of the ocean? [Answer: In the middle of the Atlantic Ocean, two plates are pulling apart from each other. Where these plates pull apart, new lava rises up and cools. This lava is younger than the rock to either side.

[Questions 1-3: pp. 202s, 200-201t]

4.       How does the theory of plate tectonics explain why the continents are moving? [Answer: The theory of plate tectonics explains that the continents are moving because they are part of moving plates that cover the earth's surface.]

5.       How does plate tectonic movement explain the formation of volcanoes? [Answer: Plate tectonic movement explains the formation of volcanoes in at least two ways:

a.       Where one plate sinks beneath another, the sinking plate melts, magma rises, and eventually escapes through the top of the upper plate. Volcanoes form where the molten rock escapes.

b.       Where plates spread apart, lava rises up and volcanoes form (such as on the ocean floor).]

6.       Use the theory of plate tectonics to explain the correlations you saw between the locations of volcanoes and earthquakes. [Answer: The correlation between volcanoes and earthquakes is that often they both occur in the same locations. Typically both occur along plate boundaries. For example, both earthquakes and volcanoes occur at trenches at ridges. Volcanoes are less common along transform faults.]

[Questions 4-6: pp. 204s, 201t]

However, since some of the required answers are not provided in the reading, it is not clear how students will come up with these answers or make the connection between the evidence and the explanation.

Occasionally, the text misrepresents the nature of science. For example, the text states that "to test his theory of continental drift, Wegener used a very simple analogy. He pointed out that if a sheet of newspaper is torn in half leaving jagged edges, we should be able to fit it back together based on its shape as if it were a puzzle" (p. 199s). This may leave the impression that developing an analogy is an adequate way to test a theory.  Also, some of the conclusions drawn from the evidence do not seem logical. For instance, the text explains that "scientists found tropical plant fossils on ice-covered Antarctica. This evidence indicated to some geologists that at one time the continents were much closer together and more similar" (p. 201s). However, the logical conclusion from the evidence provided is that either the climate of Antarctica has changed dramatically or the location of Antarctica has changed dramatically.


Patterns of Change presents most of the key Earth science ideas. However, one of the most important ideas-the idea that the surface of the Earth is continually changing (Idea a)-is not addressed. In many ways, this key idea is a precursor to the other ideas that  explain how the surface of the Earth changes. These other ideas (Ideas b-h) may be less credible for students if they do not understand that the Earth continually changes.

For the idea that several processes contribute to the changing surface of the Earth (Idea b), very few Earth-changing processes are discussed. Although the emphasis of chapter 10 is on the more abstract process of plate tectonics, directly observable processes such as weathering, erosion, and deposition are not mentioned.

For the other ideas, many of the experiences are not tied together. For example, the text gives examples of both abrupt (volcanic eruptions and landslides) and very slow processes (movement of tectonic plates), but presents them about 40 pages apart and never discusses or compares the range of rates of Earth-changing processes.

The material makes a serious effort to relate key Earth science ideas to their historical development and to the nature of science. Ideas about the nature of science are introduced earlier in unit 2-in Chapter 8: Scientific Explanations Begin with a Question. They are  then developed in the next two chapters in the context of presenting the key Earth science ideas. However, the primary learning goals seem to be those related to the nature of science. Key Earth science ideas seem to be used to develop nature of science ideas, as explained in the Teacher's Edition:

In this unit, the students study the nature of science by exploring the theory of plate tectonics and its relationship with associated patterns on earth. The theory of plate tectonics is an excellent vehicle for learning about the nature of science because it exemplifies key features of the scientific enterprise. [p. 141at]

Ancient and disregarded ideas about earthquakes and volcanoes are presented alongside current scientific ideas. Unfortunately, students are not given much help in distinguishing between the ideas presented until much later. Hence, the structure and sequence of lessons in this unit may work against student understanding of these key Earth science ideas.

Beyond Literacy

While the text does a nice job of restricting its treatment of this topic to key ideas and terms that are part of science literacy, its presentation of the key Earth science ideas near the beginning of grade six (level A, unit 2) seems too early for most students to follow. While National Science Education Standards (National Research Council, 1996) includes these key ideas in content standards for grades 5-8 (pp. 159-160), Benchmarks for Science Literacy (American Association for the Advancement of Science, 1993) postpones the theory of plate tectonics and its explanation in terms of heat convection, gravity, and density until grades 9-12 (p. 74). Without an understanding of how moving plates can be explained by underlying physics principles, the theory may seem to have been pulled out of thin air. In addition, the historical presentation of the key ideas adds further sophistication because students are expected to follow the logic as the story unfolds (even though few scientists did so at the time). The Teacher's Edition provides no rationale for treating this topic so early.


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 Earth science examples of the kinds of misleading illustrative materials of most concern to the evaluation teams:

  • Maps that do not show the accurate locations of earthquakes and volcanoes will prevent students from understanding the relationship between these events and plate boundaries. Likewise, diagrams and maps that do not include legends, and photographs that do not explain the size and scale of the object seen, are difficult for students to understand.

  • Diagrams that (a) depict plates moving away from one another, thus exposing the mantle, (b) show the mantle very close to the surface of the Earth, or (c) show plates as being a layer under the crust inaccurately represent the structure of the Earth and the motion of plates.
  • Diagrams that show the melting of subducted plates are incorrect. Subducting plates are known to cause melting in the mantle, and thus nearby volcanic activity, but the plates do not melt.