Adolescent growth and development are influenced by various environmental factors in Nairobi slums, where access to nutritious food is often limited. A longitudinal study was conducted with adolescents aged 10-18 years from four randomly selected Nairobi slums. Participants were recruited through community health workers, and data collection included anthropometric measurements at baseline and follow-up. Height-for-age z-scores improved by an average of 0.2 SD units post-intervention (95% CI: 0.1-0.3), indicating a moderate beneficial effect on growth trajectory. Nutrition interventions were effective in promoting adolescent growth, particularly height development, but further studies are needed to explore long-term outcomes and cost-effectiveness. Public health policies should prioritise nutrition education and access to affordable nutritious foods for adolescents living in Nairobi slums. Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.