Students often hold strong attitudes regarding topics they encounter during their studies, and many instructors feel that these attitudes can have strong effects on students' performance. We characterized students' attitudes toward evolution and investigated the influence of students' attitudes (precourse and post-course) regarding evolution on their performance in an evolution course, measured as their final grade. We found our students to hold positive attitudes toward evolution; these attitudes became more positive following the course. The most significant change in attitude occurred in the group of students initially undecided toward evolution. We also found that attitudes prior to the course had little influence on later achievement; however, at the end of the course, students' attitudes were positively related to final grades, although the effect was small. We argue that pedagogical techniques directly addressing students' attitudes help reduce the influence of attitudes (especially prior attitudes) on achievement. Anecdotal evidence from instructors has suggested that students' attitudes toward the subjects they study influence their performance in those subjects. In his meta-analysis of research investigating relationships between attitude and achievement, Willson (1983) concluded that attitude had a modest effect on later achievement for college students. However, recent research has been equivocal with respect to the relationship between attitude and achievement in science courses. For example, Willson, Akerman, & Malave (2000) found no association between students' attitudes and their later achievement in a college physics course. Similarly, Nicoll & Francisco (2001) reported that students' attitudes about math ability and about a particular course did not predict achievement in college-level physical chemistry. In contrast, Freedman (1997) found that attitude was positively and moderately correlated with achievement for high school