Theories of change propose how intervention resources and activities might lead to the generation of outcomes. They are sometimes presented diagrammatically as logic models. Realist evaluators and others have suggested that interventions should be theorised in terms of how intervention mechanisms interact with context to generate outcomes. Our own trial of the Learning Together whole-school intervention to prevent bullying set out to define, refine and test such theories in the form of context–mechanism–outcome configurations (CMOCs). We drew on several sources to define our starting CMOCs. These included existing middle range theory. This is scientific theory about the general mechanisms (i.e. not necessarily concerning an intervention) that generate outcomes. This should be analytically general enough to apply to a range of settings, populations and/or outcomes, but specific enough to be useful in a given application. We also used previous research and public consultation to inform our CMOCs.