Objective: To consider the short- and medium-term impact of a school-based exhibition of prevention materials designed by adolescents in human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) knowledge and attitudes and in the school's involvement in health education. Design: Mixed-methodology that combines quantitative and qualitative methods to consider short- and medium-term impact of a school-based HIV prevention project. Setting: Thirteen basic and secondary schools across Portugal, randomly selected. Method: A one-group pre-posttest design study in 13 schools addressing changes in adolescents' HIV/AIDS knowledge and attitudes as mediated by gender and age, followed by a replicated field study design. Expert interviews and focus groups with teachers, school staff, students, and parents to explore medium-term impact. Results: The project was effective in promoting students' AIDS-related knowledge and attitudes, especially for girls and younger adolescents. The project also inspired the participating schools to develop initiatives in the field of AIDS education. Conclusions: The paper demonstrates how AIDS education in the school context can be effective, but research must guarantee the quality of data collection instruments, consider the diversity and heterogeneity of adolescents as a target group, and disseminate the project's results in the school's context. (Contains 1 table and 2 figures.)