Urban adolescents in Lagos, Nigeria face significant mental health challenges due to socioeconomic pressures and limited access to care. A comprehensive search of databases including PubMed, Scopus, and Google Scholar was conducted using keywords related to mental health, adolescent education, and Nigeria. Studies published between and were included if they reported outcomes from school-based interventions targeting urban adolescents in Lagos. A total of 82 studies met inclusion criteria; however, only 14 provided three-month post-intervention data for analysis. The proportion of participants showing significant improvements ranged from 45% to 60%, with qualitative themes indicating positive impacts on mental health literacy and coping skills. School-based interventions appear effective in improving mental health outcomes among urban adolescents, though variability exists across studies. Future research should focus on replicating successful interventions, conducting longitudinal evaluations, and addressing implementation challenges to ensure scalability and sustainability. Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.