School improvement remains a central concern for education systems worldwide as they strive to enhance equity, quality, and student engagement. Cooperative learning defined as structured small-group pedagogy in which students work together to maximise their own and each other's learning has been widely promoted for its potential to improve academic outcomes, social skills, motivation, and learner autonomy. Despite strong evidence of its benefits, the implementation and impact of cooperative learning are highly contingent on policy environments, institutional structures, and classroom realities. This paper critically examines cooperative learning as a school improvement strategy through a qualitative research synthesis of international literature from high-income and low- and middle-income contexts. The study analyses how cooperative learning is framed in national and regional policy documents, enacted at classroom and school levels, and mediated by teacher practices, professional development, assessment systems, and cultural norms. Findings indicate that while cooperative learning consistently supports positive academic and social outcomes, its transformative potential is frequently constrained when treated as an isolated classroom technique. Effective enactment requires alignment across multiple system levels, including curriculum design, assessment practices, sustained teacher learning, and leadership support. Systems that provide coherent policy backing, collaborative professional learning, and supportive school cultures enable cooperative learning to function as a whole-school improvement strategy. The paper concludes by proposing a Policy-Aligned Cooperative Learning Framework, integrating curriculum alignment, assessment coherence, professional development, and instructional leadership. This framework provides a practical and conceptual guide for policymakers, school leaders, and educators seeking to embed cooperative learning within sustainable, context-responsive school improvement initiatives.