ABSTRACT The burden of pediatric mental, neurological, and substance disorders in low-and middle-income countries (LMICs) is tremendous. Although progress has been made over the past decade in applying task-shifting approaches to scale evidence-based intervention (EBIs) in schools in LMICs, there is more to be learned about the most effective and efficient ways to scale and sustain school-based EBIs in LMICs to support child mental health, including both horizontal scale-up (processes for supporting and sustaining high-quality EBI implementation in schools across regions and nationally) and vertical scale-up (processes for institutionalizing and championing the EBI through policies and practices at all levels of the educational system). The overarching goal of this project is to address these knowledge gaps by studying vertical and horizontal strategies for scaling and sustaining one EBI to promote child mental health in Uganda. The EBI in this study is ParentCorps-Professional Development (PD), a universal school-based preventive EBI that trains and supports teachers to apply evidence-based strategies to promote children’s mental health, and to share prevention knowledge and skills with parents. This task-shifting model of mental healthcare shifts activities from professionals to teachers to promote children’s mental health. Effectiveness-implementation studies conducted in Uganda and Nepal have demonstrated the effectiveness of task-shifting, with positive impacts on children, teachers and schools. Results were similar when using a train-the-trainer model where ParentCorps-PD was implemented by mental health professionals compared to when the PD was implemented by trained tutors (non-mental health professionals) from Teacher-Training Colleges’ (TTCs). A combination of teacher task- shifting and TTC train-the-trainer model offers a more scalable and sustainable approach for the educational system in LMICs. The proposed study builds on this work and tests new horizontal and vertical scale-up strategies to develop national and regional systems to support ParentCorps-PD implementation in Uganda. The Specific Aims are to: 1) examine how a vertical scale-up strategy (leadership advocacy strategy) leads to changes in policy, practice, or scale-up of EBIs; 2) support policy-research-practice partners (from Aim 1) to make strategic choices and formalize implementation blueprints for scaling-up ParentCorps-PD; 3) examine regional training-centers (TTC) and school PD implementation and practice outcomes when the new optimized package of the ParentCorps-PD scale-up implementation blueprint (from Aim 2) is implemented; and 4) explore the underlying scale-up and sustainability implementation mechanisms to inform the development of a full high-quality scale-up implementation framework and processes relevant to low-resource and LMIC settings.