Adolescent mental health problems are prevalent in low- and middle-income countries, like Kenya, where access to care remains severely limited. Task-shifted, school-based interventions offer solutions but often lack structured protocols for managing risk, such as suicidality or abuse. The Shamiri Risk Management Protocol (Shamiri-RMP) was developed to address this gap through a tiered system for screening, classifying and responding to risk within a stepped-care mental health model. We conducted a mixed-methods implementation study across 149 public high schools in Kenya. Caseworker fidelity and risk classification accuracy were evaluated through a review of 222 student cases. The Consolidated Framework for Implementation Research guided the qualitative analysis of caseworker surveys to identify implementation barriers and facilitators. Of 76,855 students enrolled in the broader Shamiri program, 977 (1.27%) were referred for risk assessment, and 222 (0.28%) were enrolled in the Shamiri-RMP. Among them, 42.71% were low-risk, 35.68% moderate-risk and 21.61% high-risk. Risk reductions occurred in 60.47% of high-risk cases, 56.34% of moderate-risk cases and 51.76% of low-risk cases. Implementation facilitators included supervisory support (50.88% of caseworkers) and protocol clarity (80.70%), while barriers included referral gaps (5.26%) and confidentiality concerns (54.39%). Findings support the feasibility and scalability of the Shamiri-RMP in low-resource school settings.