Purpose: Systems educational reform in developing countries through effective principal capacity- building programs is essential for improving student learning, with the purpose of this paper being to use case studies to identify key success factors in the implementation of an instructional leadership program in the developing country of Kiribati. Design/methodology/approach: A case study approach involving mixed methods including semi-structured interviews and document analysis was used within three purposively sampled schools to examine implementation success factors relevant to instructional leadership literature. Findings: The case studies reveal the overall value of the Kiribati instructional leadership program involving school leader workshops and ongoing coaching support, with instructional leadership reflecting directive and collaborative, as well as transformative theoretical aspects. Key implementation success factors within researched schools were leaders undertaking regular observations in classrooms, systematic tracking of student achievement and nurturing a positive culture for learning, as well as establishment of various collaborative processes involving community and teacher peer learning groups. Research limitations/implications: The study provides in-depth information through teacher and school leader interviews and examining relevant school documentation artefacts. A limitation is that the study involved only three schools and was undertaken less than a year into program implementation. Future research involving more schools and several years after implementation would be beneficial to investigate sustainability across the school system and longer-term program impacts. Practical implications: The data provides practical tips for school leaders regarding effective teacher capacity-building approaches, as well as providing information for policy makers, especially in developing countries, about effective professional development programs for school leaders and teachers. Originality/value: The study examines a system-wide workshop series and coaching approach to school leader and teacher capacity-building in a developing country from a theoretical and practical perspective relevant to instructional leadership and also transformational leadership, which is an under-researched area.