Charter schools have been promoted internationally as a governance reform intended to improve student achievement through increased operational autonomy combined with public accountability. While extensive empirical research has examined charter school effectiveness in decentralized education systems, comparatively little is known about how charter reforms function within highly centralized, inspection-led accountability environments. This study examines the impact of charter schools on student achievement in Abu Dhabi using a mixed-methods design anchored in the Abu Dhabi Department of Education and Knowledge (ADEK) Inspection Framework. The study integrates inspection outcomes aligned with the official ADEK performance standards, teacher and school leader perception data, and qualitative evidence to examine how charter governance operates through mediating mechanisms rather than direct effects. Inspection judgements related to Teaching and Learning (PS1), Student Achievement (PS2), Leadership and Management (PS3), Behaviour and Wellbeing (PS4), and Overall Effectiveness (PS5) are analysed alongside survey measures of instructional leadership, organizational capacity, behaviour management systems, policy enactment, and stakeholder pressure. Quantitative analyses are presented as illustrative pilot findings to demonstrate analytic feasibility in a data-constrained context, while qualitative findings provide theory-driven explanations of observed patterns. Findings indicate that charter school performance in Abu Dhabi is highly variable and that differences in inspection outcomes are more strongly associated with leadership capacity, behaviour management, and organizational conditions than with charter status per se. Behaviour and Wellbeing (PS4) emerges as a persistent system-level constraint, with implications for teaching quality and achievement. The study contributes a contextually grounded evaluation framework for charter school reform in centralized education systems and offers policy-relevant insights for system leaders seeking to align autonomy, inspection, and sustainable school improvement.