Claims about teachers' potential to influence change tend to overlook that educational outcomes arise from complex, situated practices of many actors including teachers. This article introduces a tool for Teachers' Reflection on their Agency for Change (TRAC) for empirical analysis of teaching as a collective activity designed to 'track' the diverse outcomes of teacher agency, including but not limited to student attainment, while accounting for the relational and institutional contexts. Activity theory is applied to map purposes and contexts of teacher agency. Uses of TRAC in professional development and inquiry are illustrated with an example of one teacher's reflection during her collaboration with researchers on a change project aimed at 'closing the attainment gap'. Inclusive pedagogy is used as an interpretative lens to discuss agency in relation to its specific purpose and context. The article offers guidance for future uses of TRAC to consider teachers' impact on any change agenda.