What Educational reforms around the world have resulted in significant pressures on school principals to improve student outcomes. The most recent Danish school reforms also reflect this global tendency, ascribing school principals primary responsibility for developing school practices to promote student achievement and well-being. In such a context, this project explores the relationship between school leadership and student outcomes in different national contexts, including Denmark, in terms of both achievement and well-being, before examining the reasons for the identified relationships in an exclusively Danish context. Why In recent years, research on the relationship between leadership and student outcomes has been growing in line with the increasing accountability demands. However, such research still has several drawbacks. First, most existing studies are based on small data sets with few variables. Second, there has been a lack of international comparison, mostly because of the unavailability of cross-national data including information on both leadership and student outcomes. Third, there have been only a few mixed-methods studies, which combine quantitative and qualitative approaches. The results of this project focusing on the role of school leadership in student achievement and well-being in different national contexts will be of great interest to an international audience. How This study employs an explanatory mixed-methods design, in which qualitative analysis is conducted after quantitative analysis. Quantitative analysis will be based on two large-scale OECD studies (TALIS and PISA). The qualitative part will will be based on semi-structured interviews and shadowing techniques with the aim of better understand and explain the nature of relationships identified by the quantitative part. SSR Academic achievement and well-being of the new generations are greatly related to the development and welfare of the societies. Leadership has been one of the understudied factors, which can foster student achievement and well-being at schools. By focusing on the effects of leadership, this research project will contribute social development and cohesion by identifying the currently missing mechanisms for the improvement of student achievement and well-being.