In this study, the professional learning of two groups of secondary mathematics teachers are compared as they participate in an education research project to explore the uses of iPads within formative assessment processes. Data from lesson observations, meetings and teacher interviews show how collaborative participation in a design research cycle involving the development, implementation and analysis of lessons facilitated individual and collective professional learning. Specific elements of the design research process provided opportunities for knowledge sharing and reflection on practice, but individual learning gains were closely associated with the development of these teacher groups into professional learning communities. Two contrasting case studies show how various affordances and constraints of the research activity either encourage or restrain the development of characteristics associated with professional learning communities. The findings provide insight into the early developmental stages of professional learning communities, the conditions that affect their growth and the efficacy of collaborative design research to stimulate the development of such communities.