Internationally teachers are called upon to act as agents of change. However, there is little clarity about the kind of change teachers are expected to contribute to and even less empirical evidence about the ways teacher agency operates in schools and beyond. Empirical analyses of teacher agency require a clear articulation of the purpose and content of such agency in relation to a particular aspect of change, which could then help us specify appropriate units of analysis and generate hypotheses based on the insights provided by previous research. This paper articulates a model for study of teacher agency as a process whereby teachers act strategically to transform the risks of exclusion and underachievement into inclusion and improved outcomes for all students in contexts of cultural and social diversity. The model is guided by social theories of human agency within social structures and cultures, applied to the empirical insights into teachers' inclusive practices. Potentially appropriate units of analysis and related variables are proposed, and face-validated in consultation with 12 experts from Scotland including teachers, (deputy) head teachers, researchers, teacher educators and policy-makers. The units include teachers' inclusive practices at individual, school and broader policy and social levels, teachers' moral purposes and competence as agents of change for inclusive education, scope of teachers' autonomy including individual, collective and contextual variables, and teachers' reflexivity. Implications for future research and teacher education are discussed.