Background: This article focuses on the complementarity between formative interventions research conducted within the framework of cultural historical activity theory, action research and learning, as well as how this complementarity influences the researcher's role. Purpose: The study suggests how action research, learning and formative interventions can be complementary in educational research and, furthermore, how this complementarity can challenge and expand the researcher's role when supporting and researching school development processes. Sources of evidence: A previously conducted study is presented as an example. The analysis of the researcher's role is based on observations, interviews, reflection conversations and questionnaires focusing on the arenas in which the researcher acted. Main argument: The paper argues that the researcher's role in educational research should be expanded, combining the researcher's role both in action research and in formative interventions. The example study shows that researchers must engage with teachers in their teaching and support them in their daily practice, thus helping them to apply new knowledge to practical situations in order to develop their practice. Conclusions: Complementarity between action research, action learning and formative interventions aligns the processes at the classroom and system levels, leading to school development.