We report results from a randomized evaluation comparing three school-based HIV/AIDS interventions in Kenya: 1) training teachers in the Kenyan Government's HIV/AIDS-education curriculum; 2) encouraging students to debate the role of condoms and write essays on how they can protect themselves against HIV/AIDS; and 3) reducing the cost of education. Our primary measure of the effectiveness of these interventions is teenage childbearing, which is associated with unprotected sex. We also collected measures of knowledge, attitudes, and behavior regarding HIV/AIDS. After two years, teacher training increased students' tolerance toward people with HIV/AIDS. Girls exposed to the program were more likely to be married to the fathers of their children. The program had little other impact on students' knowledge, attitudes, and behavior, or on the incidence of teen childbearing. The condom debates and essays increased practical knowledge and self-reported use of condoms without increasing self-reported sexual activity. Reducing the cost of education by paying for school uniforms reduced dropout rates, teen marriage, and childbearing.