Adolescent sexual behaviors in South African high schools are influenced by various factors including school-based HIV prevention programmes. An ethnographic approach was employed to gather in-depth qualitative insights from adolescents, educators, and programme administrators. Data collection included interviews, focus groups, and document analysis. A significant proportion (70%) of participants reported positive changes in sexual behaviour after participating in the programmes, with a notable decrease in unprotected sex practices. School-based HIV prevention programmes appear to have a positive impact on adolescent sexual behaviors, though further research is needed to understand long-term effects and contextual factors. Longitudinal studies should be conducted to evaluate the sustainability of these interventions over time. Additionally, incorporating feedback from adolescents into programme design could enhance their relevance and effectiveness. Adolescents, HIV prevention programmes, sexual behaviors, school-based interventions, ethnographic study