ABSTRACT: This project assessed the impact of a school-based AIDS prevention program on student participation in sexual risk and protective behaviors such as use of condoms and use of condoms with foam and intention to participate in such behaviors. The paper focuses on students who became sexually active for the first time between the seventh and eighth grade (“changers,” n = 312). The school-based intervention was developed using social cognitive theory and the social influences model of behavior change. Using an experimental, longitudinal design, 15 high-risk school districts were divided randomly into two treatment (10 districts) and one control (five districts) conditions. Students in both treatment conditions received a 10-lesson classroom program in the seventh grade with a five-lesson booster in the eighth grade, while control students received basic AIDS education (current practice in their districts) in compliance with state mandates. Results indicated classroom programs had an impact on certain protective behaviors and on frequency of sexual activity the past month. Post-intervention measures also indicated the program affected students' intentions to perform specific protective behaviors.