Constructivist teaching techniques work well in various instructional settings, but many teachers remain skeptical because there is a lack of quantitative data supporting this model. This study compared an undergraduate nonmajors biology lab section taught in a traditional teacher-centered style to a similar section taught as a constructivist class. Weekly lab quiz scores, attendance, a science attitude inventory, and an analysis of videotapes were used to determine whether student interest and performance were affected by the teaching style used. Evaluative tests showed many significant differences between the groups and demonstrated that the constructivist class had higher quiz scores, more appreciation of science, better attendance, and increased participation in the lab activities than the traditional group. (Contains 2 tables and 3 figures.)