This cross-sectional study describes three approaches to sex education in schools in three locations-- Rio de Janeiro, Belo Horizonte, and Salvador, all in Brazil. It compares knowledge, attitudes and practices related to sexuality, citizenship and gender among adolescents in schools with such programs, compared to controls in schools without them. Results show that the program in Salvador improved knowledge on sexuality and reproductive physiology, attitudes towards citizenship, and use of modern contraceptives compared to controls. In Rio de Janeiro, participants had improved knowledge of reproductive physiology and attitudes towards sexuality. In Belo Horizonte, participants increased their knowledge of reproductive physiology and STI/HIV prevention, but still had less positive attitudes regarding gender, and reported increased sexual activity. In Salvador, the focus was more on creative and cultural activities, while Belo Horizonte's program lacked interaction with health services and providers.