School-based sexuality education programmes have been implemented in Ghanaian cities to improve adolescent reproductive health outcomes. A longitudinal cohort study design was employed, with data collected annually from to . A total of 500 participants were recruited at baseline and followed up for three consecutive years. Data collection included self-reported surveys, biological samples, and health check-ups. In the third year of follow-up, a significant decrease in reported unprotected sexual intercourse (64% vs. 78%) was observed among those exposed to the programme compared to non-exposed groups. The school-based sexuality education programmes had a positive effect on reducing risky sexual behaviors and improving reproductive health outcomes. Further research should investigate long-term effects and explore scalable implementation strategies for broader population coverage. Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.