A two part study investigated any relationship between student achievement and textbook content as well as any impact of a national project's recommendations on textbook content. First, analyses of student responses to biological items on the 1977 National Assessment of Educational Progress's survey of science showed a direct, linear relationship between achievement level and concept emphasis in biology textbooks. Second, a comparison between biology textbooks, published a decade apart, indicated significant changes in the degree of emphasis placed on 10 commonly accepted conceptual areas. Closer examination revealed that change in the amount of emphasis in one conceptual area, Growth and Development, was responsible for the significant difference found. Generally, the recommendations of the biology project were not reflected in the newer textbooks.