The question addressed in this paper is whether the beneficial effects of Primary School Action for Better Health (PSABH), an HIV prevention programme delivered in Kenyan primary schools, continue once students move on to secondary schools. Questionnaires were completed in December 2005 and January 2006 by all form 1–3 students in 154 randomly selected secondary schools. Students who had attended primary schools with PSABH programming were compared to those who did not on knowledge, attitudes and behaviours using multivariate regression with controls for gender, school year, religion and financial resources. Students who attended PSABH primary schools were significantly more likely to have higher levels of knowledge and attitudes that were more supportive of sexual restraint, condom use and HIV testing. They were more likely to have used several safer sex practices and to have been tested for HIV. The effects were strongest in the first year of secondary school and decreased thereafter. PSABH continues to have a beneficial effect for students who continue to secondary school.