HIV prevalence among secondary school boys in Dar es Salaam, Tanzania remains high despite existing prevention programmes. A randomized controlled trial was conducted with a sample of 500 male students, randomly assigned into an intervention group (n=250) and a control group (n=250). Data collection included pre- and post-intervention surveys and behavioural observations over three years. During the follow-up period, there was a significant reduction in unprotected sexual behaviors among those who received the HIV prevention intervention compared to controls. Specifically, the proportion of boys engaging in unprotected sex decreased by 20% (p < 0.05). The study demonstrated that sustained engagement with HIV prevention interventions can lead to lasting behavioural changes and improved knowledge about HIV transmission among secondary school-aged males. Future research should consider scaling up these successful intervention models across broader populations in Tanzania and replicate studies in other African countries.