This academic review critically examines the theoretical and empirical bases of claims made for the educational benefits of physical education and school sport (PESS). An historical overview of the development of PESS points to the origins of claims made in four broad domains: physical, social, affective and cognitive. Analysis of the evidence suggests that PESS has the potential to make contributions to young people's development in each of these domains. Unsurprisingly, perhaps, there is suggestive evidence of a distinctive role for PESS in the acquisition and development of children's movement skills and physical competence. It can be argued that these are necessary, if not deterministic conditions of engagement in lifelong physical activity. In the social domain, there is sufficient evidence to support claims of positive benefits for young people. Importantly, benefits are mediated by environmental and contextual factors such as leadership, the involvement of young people in decision-making, an emphasis on social relationships, and an explicit focus on learning processes. In the affective domain, too, engagement in physical activity has been positively associated with numerous dimensions of psychological and emotional development, yet the mechanisms through which these benefits occur are less clear. Likewise, the mechanisms by which PESS might contribute to cognitive and academic developments are barely understood. There is, however, some persuasive evidence to suggest that physical activity can improve children's concentration and arousal, which might indirectly benefit academic performance. It can be concluded that many of the educational benefits claimed for PESS are highly dependent on contextual and pedagogic variables, which leads us to question any simple equations of participation and beneficial outcomes for young people. In the final section, therefore, the review raises questions about whether PESS should be held accountable for claims made for educational benefits, and about the implications of accountability.