We evaluated Simulations in Developmental Disabilities (SIDD), a multimedia software program that provides students with practice in behavioral assessment and treatment decisions for persons with developmental disabilities. Following a lecture on clinical strategies, students in an experimental group received instruction with SIDD whereas students in the control group did not. We collected assessments of students' clinical knowledge before and after the lecture, immediately after training, and several weeks later. The lecture had no immediate impact on clinical knowledge; however, there was a significant difference in test scores between the experimental group and the control group following exposure to SIDD training, which remained at follow-up.