This ADEA-commissioned study provides an in-depth mapping of 12 key development partners engaged in capacity development for system-level leadership and management in K-12 education across low and lower-middle income countries, with a focus on Sub-Saharan Africa. It examines how organizations such as the World Bank, GPE, UNESCO-IIEP, USAID, and others define, prioritize, and implement capacity development interventions. The study identifies six primary activity types - training, technical assistance, infrastructure support, research and assessment, knowledge exchange, and multi-modal initiatives. It also highlights conceptual frameworks used by each institution and their approaches to measuring effectiveness. While many efforts focus on localized project-related capacity, challenges remain in achieving systemic, sustainable improvements. Notably, shared principles emerge across partners, including the need for long-term engagement, local ownership, evidence-based strategies, and responsiveness to political and institutional contexts. The report calls for greater coordination, investment in middle-tier leadership, and a shift from fragmented to holistic approaches. It offers actionable insights for ADEA and stakeholders aiming to drive transformative, scalable improvements in education system governance and leadership.