This study demonstrates a small, but significant, difference in prior understanding of basic biological concepts between students enrolled in majors' versus nonmajors' introductory biology courses. By the end of their respective courses, nonmajors demonstrated greater improvement in posttest scores than did majors. Furthermore, although initially students in the major course had a significantly more positive attitude towards science, especially in terms of personal comfort with science, by the end of the course this difference disappears. Following a semester of instruction, the attitudes of nonmajors generally improved, but student attitudes in the majors' classes declined in nearly all categories. We demonstrate a significant instructor effect in these results.