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Middle and High School Science Textbooks
A Standards-Based Evaluation

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Does the material specify prerequisite knowledge/skills that are necessary to the learning of the key idea(s)?

Explanation. This criterion refers to conceptual prerequisites to key ideas (which are typically found on a relevant strand map) that are common to all materials, and those prerequisites that arise out of the ways in which particular materials present key ideas.

Common prerequisites. Understanding key ideas often requires that students first understand some other "prerequisite" ideas. For example, knowing what molecules are is prerequisite to understanding that food provides molecules that serve as fuel and building material for all organisms; and knowing what fossils are and how they are formed precedes understanding that fossils provide evidence for descent from common ancestors.

To identify prerequisites for key ideas, it is helpful to check relevant strand maps in Atlas of Science Literacy (AAAS, 2001). The maps in Atlas are built from benchmarks—the learning goals presented in Benchmarks for Science Literacy. Benchmarks itself was derived from the adult literacy goals in Science for All Americans. The connections among benchmarks that are made in the maps are based on the cognitive research and essays in Benchmarks, and on the account of adult literacy in Science for All Americans. For example, the idea that "…Different arrangements of atoms into groups compose all substances" is shown as contributing to the idea that "Food provides molecules that serve as fuel and building material for all organisms" (Atlas, p. 77). The grades 6–8 essay on Flow of Matter and Energy suggests: "Before [students] have an understanding of atoms, the notion of reusable building blocks common to plants and animals is quite mysterious. So following matter through ecosystems needs to be linked to their study of atoms" (Benchmarks, p. 120). The same strand map also shows the idea that "Air is a substance that surrounds us and takes up space" as contributing to the idea that "Plants use the energy from light to make sugars from carbon dioxide and water." Notes that accompany the map indicate that "For students to understand that plants take something out of the air to make food, they need to believe that air is a substance (that plants are not making food out of nothing or solely from soil and water)" (Atlas, p. 76). Chapter 15: The Research Base in Benchmarks (p. 335) suggests that with special instruction, students in grade 5 can identify the air as the final location of evaporating water, but they must first accept air as a permanent substance.

Material-specific prerequisites. In addition to prerequisites to specific key ideas, additional prerequisites may arise from the approach taken in a particular material or from specific activities it uses. For example, consider the idea that "Spreading data out on a number line helps to see what the extremes are, where they pile up, and where the gaps are" (Atlas, p. 123). In addition to the conceptual prerequisite shown on the map that "Numbers can be used to count things, place them in order, or name them," a material might introduce new prerequisites because some activities require measurement skills.

For the analysis of middle grades science and high school biology textbooks, reviewers were given strand maps of key ideas and their conceptual prerequisites. (See, for example, the map provided for Matter and Energy Transformations.) Reviewers were then asked to (a) identify any instructional prerequisite ideas or skills, (b) examine whether the material alerts teachers to either common or material-specific prerequisites and to what they are needed for, (c) examine whether the material alerts students to prerequisite ideas or experiences that are being assumed, (d) examine whether the material has adequately addressed the prerequisites (that is, has provided instructional support for them as opposed to merely stating them), and (e) examine whether the material is explicit in helping students move from prerequisites to key ideas. While a stand-alone unit should not be faulted for not addressing prerequisite ideas or skills, it should be expected to make connections between key ideas and their prerequisites. Similarly, while it is not reasonable to expect a material to teach prerequisites from an earlier grade level, it is reasonable to expect a material to help students to move from the prerequisites to the key ideas being taught.

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