Recent research suggests that a major obstacle to evolution understanding is an essentialist view of the biological world. The present study investigated the effects of formal biology instruction on such misconceptions. Participants (N = 291) completed an assessment of their understanding of six aspects of evolution (variation, inheritance, adaptation, domestication, speciation, and extinction) before and after one of six evolutionary-themed courses. Most participants demonstrated pervasive misconceptions at both pretest and posttest. A subset, however, demonstrated reliable pre-post gains, and they differed from their peers in that they (a) began the semester with significantly less accurate, yet significantly more consistent, views of evolution, and (b) ended the semester with significantly less consistent, yet significantly more accurate, views of evolution. These findings indicate that naive theories of evolution, while generally resistant to change, are less resistant the more consistent they are, possibly because consistency highlights limitations in their explanatory power and inferential scope. (Contains 2 tables and 3 figures.)