PROJECT SUMMARY This study will examine a new implementation strategy for the Youth Readiness Intervention (YRI), an evidence-based mental health intervention. The strategy will (a) leverage a delivery setting (schools) and workforce (teachers) used effectively in low- and middle- income countries; and (b) innovate with technology and mHealth tools to enhance mental health service delivery quality. The YRI will be implemented as an extracurricular resilience-building afterschool activity in Sierra Leone. Teachers will deliver the YRI and receive either mobile phone-supported supervision or standard in-person supervision. Mobile-based supervision will integrate WhatsApp, a free cross-platform messaging and voice service used widely throughout Africa, with a new mHealth app. The mHealth app was recently designed to support fidelity monitoring of Sierra Leonean lay workers delivering the evidence-based Family Strengthening Intervention (R21MH124071). The mHealth app will support supervision through key features, including voice activated content, fillable forms (i.e., YRI fidelity checklist), visual dashboards to monitor fidelity, and training videos to support school-based YRI delivery. The Exploration, Preparation, Implementation, Sustainment (EPIS) framework, a broad multilevel, context- sensitive implementation science model, will guide the study. A hybrid type 3 implementation-effectiveness design will allow for evaluation of both mobile phone-based supervision as a new implementation strategy, and clinical effectiveness of the YRI on youth mental and behavioral health as secondary outcomes. Aim 1 (Exploration and Preparation) will investigate barriers and facilitators to successful YRI implementation aided by mobile-based tools in Sierra Leone’s secondary schools. A mixed methods evaluation with teachers, principals, and government ministry officials will inform co-development of an implementation blueprint prior to YRI delivery. User-centered design methods will be used to adapt the mHealth supervision app and incorporate WhatsApp to create an integrated user model of mobile phone-based supervision. Aim 2 (Implementation) will examine the feasibility, acceptability, cost, and fidelity to the YRI delivered by teachers receiving mobile-based supervision compared with those receiving standard supervision via a mixed methods approach. Aim 3 (Impact of Delivery Approach on YRI Effectiveness) will compare the effectiveness of the YRI in improving mental health, emotion regulation and daily functioning in youth (aged 14-24) when delivered in school settings by teachers who receive either mobile-based supervision (N=480 youth) or those who receive standard supervision (N=480 youth). Aim 4 (Sustainment) will (a) investigate mechanisms of adoption and sustainment of the YRI delivered by teachers through a mixed methods evaluation with teachers, youth, and principals; and (b) conduct a cost-effectiveness and return on investment analysis to evaluate ...