tests. As already described, such tests often fail to adequately assess understanding of scientific concepts and knowledge about specific aspects of the natural world (CPRE, 1996). Moreover, most assessments evaluate the effectiveness of a student's entire learning experience; they do not distinguish between what students learn from instructional materials and the teaching centered on the materials, as distinct from what they have learned from their own activities and experiences and from their parents. There is no substantial body of research that tries to evaluate the effectiveness of particular instructional materials as a separate variable in the total learning experience. The one reasonably well-documented example of such a study evaluates a sixth grade unit on "Matter and Molecules" (Lee, Eichinger, Anderson, Berkheimer, and Blakeslee, 1993). In the absence of a substantial body of research, the use of tools such as the one described in this report will depend to some extent on the experiences that evaluators bring to the review and selection processes. Classroom experience, while informative, cannot, for many reasons, be considered definitive or unbiased. The Committee urges that extensive research on the effectiveness of instructional materials be promoted in the near future.