This paper illustrates a new way of working collaboratively on the development of a methodology for studying teacher agency for social justice. Increasing emphasis of impact on change as a purpose of social research raises questions about appropriate research designs. Large-scale quantitative research framed within externally set parameters has often been criticised for its limited potential for capturing the contexts and impacting change, while smaller, locally embedded, mostly qualitative inquiries have been questioned on the grounds of their limited generalizability and sometimes compromising research rigour. New ways of working collaboratively are increasingly explored as a way of reconciling research rigour and impact. The paper presents the procedures for designing a study that is both methodologically rigorous and potentially impactful. Twelve researchers, practitioners and policy-makers in Scotland were extensively involved in designing a mixed-method study of teacher agency for social justice. The Critical Communicative Methodology was employed to establish egalitarian dialogue between researchers and practitioners. The procedures and the resulting research tools can be used in future studies, including large-scale quantitative analysis. The paper discusses the challenges of ownership, choice of methods, and knowledge transfer, that need to be addressed in these ways of working.