The influence of a 3-week institute upon secondary biology and earth science teachers regarding their experiences with respect to the teaching of evolution was investigated. The institute directors, with National Science Foundation (NSF) funding, hoped to foster an understanding of the nature of science, provide enhanced content, and support a forum for teachers to discuss problems common to the teaching of evolution. Analysis of data indicated statistically significant increases in participants' acceptance of the theory of evolution and their understanding of both applied evolutionary principles and the applied nature of science. In addition, a significant reduction in participants' perceived anxieties regarding the teaching of evolution was achieved. Further, a qualitative examination of Stages of Concern (SoC) profiles indicated a slight shift by participants toward the use of more student-centered instruction. Finally, data were collected from 9 of the original 19 participants at a voluntary follow-up session, 8 months after the formal institute. Scores from all of the data-collection instruments (with the exception of SoC profiles) exhibited a slight decline. These decreases were not, however, statistically significant. Examination of SoC profiles, however, indicated a much stronger adoption by follow-up participants for the use of student-centered instructional strategies for the teaching of evolution.