Urban adolescent sexual health education programmes have been established in Nigerian urban areas to address high rates of sexually transmitted infections and unintended pregnancies among adolescents. A mixed-methods approach was employed, including surveys and focus group discussions with students from urban schools to assess knowledge, attitudes, and practices related to sexual health. A notable increase of 15% (p < 0.05) in students' ability to identify common sexually transmitted infections over the decade was observed. The programmes showed a positive impact on students’ knowledge about sexual health, with significant improvements in risk factor awareness and behaviour changes. Continued support for comprehensive sex education in schools is recommended, along with community-based initiatives to reinforce these messages. Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.