Urban youth in Nairobi, Kenya are at risk of contracting waterborne diseases due to poor hand hygiene practices. A cluster-randomized controlled trial was conducted with schools randomly assigned to either an intervention group (handwashing education and supplies) or a control group (no additional measures). The proportion of students practicing proper hand hygiene was significantly higher in the intervention schools compared to controls, although this varied by school type. School-based handwashing interventions showed promise in improving urban youth's hand hygiene practices and reducing waterborne disease incidence. Integrate sustained handwashing education into existing curricula and provide ongoing supplies to ensure long-term benefits. Hand Hygiene, Waterborne Diseases, Urban Youth, Nairobi, Kenya Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.