Schools are inviting settings for the promotion of healthy behaviours in children, and a number of interventions have been trialled to improve diet or increase physical activity levels with the ultimate aim of reducing the prevalence of obesity. However, these have seen mixed results and there is suggestion that consideration needs to be given to a broader definition of the school environment in order to encourage sustainable behaviour changes. This review considers evidence for associations between the physical school environment and diet, physical activity and adiposity. School environment covers the neighbourhood around the school as well as the school grounds, buildings and facilities. Reviewed evidence is used to construct a conceptual framework for understanding associations between the physical school environment and adiposity and related behaviours. The framework highlights how school environments may be modified to promote behaviour changes, and how they may limit or enhance the success of other school-based interventions. Consideration is also given to where future work may best be directed.