This thesis is concerned with understanding how the implementation of a behaviour policy in a school can be evaluated effectively. A ‘Realistic Evaluation’ approach (Pawson and Tilley, 1997) was used as a framework. Relevant literature has been identified and analysed through the process of a ‘realist synthesis’ in order to identify potential contexts and mechanisms and associated outcomes. These identified ‘context-mechanism-outcome configurations’ were used to construct eight theories regarding how students experiencing SEBD could be supported effectively by their school. The theories were tested in the study through data gathering from students experiencing a range of SEBD, their parents, teaching staff and members of the school senior leadership team. The realist interview techniques of ‘teacher-learner function’, and ‘conceptual refinement process’ (Pawson and Tilley, 1997) were used to identify contexts and mechanisms that supported the implementation of the behaviour policy. The findings from the study indicate programme self-evaluation and development in the complex social organisation of a school is more effective when it actively involves a variety of stakeholders from different levels and positions within the school community, and when it considers contextual factors at the individual, interpersonal, school and the wider social and policy level.