Active instructional approaches have been demonstrated to result in greater student achievement, prompting institutions to transition to more active learning environments. However, little work has been conducted to specifically measure the retention of knowledge gained. The purpose of the research presented here was to test assumptions regarding the effectiveness of reform-based instructional approaches at facilitating knowledge retention in students. We conducted an experimental study of knowledge retention at a midsized community college using a modified Solomon four-group design with control (lecture) and treatment (active) groups and a pre/post assessment protocol. Knowledge retention after approximately 5 months did not differ across groups. Estimated knowledge retention for the control group was slightly higher than that for the treatment group. Similarly, knowledge gains were not different across groups but other metrics such as student retention, final exam scores, and programmatic measures of student success were slightly different. We conclude by discussing the implication of our findings to the broader postsecondary science education reform movement and suggest future research to refine our incipient understanding.