PurposeCulturally responsive teaching is widely recognized as beneficial to students, especially those from historically marginalized communities. The social studies literature includes many studies of what culturally responsive teaching looks like in practice and how it can be taught to pre-service teachers. However, little is known about how in-service social studies teachers advance their knowledge and skills in this area. Studies of professional development (PD) suggest action research is a powerful format for teacher learning, but few closely examine the specific mechanisms through which action research fosters culturally responsive teaching.Design/methodology/approachThis qualitative case study of three secondary social studies teachers draws on the following data: two in-depth interviews with each teacher, audio recordings of action research meetings, project artifacts and field notes. Data were analyzed through multiple rounds of inductive and deductive coding using a codebook developed by a diverse group of researchers. The teacher participants reviewed and confirmed the findings.FindingsAll three teachers expanded their use of culturally responsive social studies instruction through systematic inquiry into their own interactions with students. The action research process fostered this growth through the following specific mechanisms: reflecting and reading independently, using data to strengthen relationships and leveraging a structure for addressing race and power in the curriculum.Originality/valueThis study illustrates how teacher action research can foster culturally responsive teaching by allowing educators to self-direct their own critical reflection and data gathering on inequities in their schools. It can also provide a structure for elevating histories that have traditionally been marginalized in standardized curricula.