This article is written from our perspective as both researchers and mathematics teacher educators, and describes how our knowledge has grown as we engage concurrently in both teaching and research. Reflection-on-action is a means for us of approaching the relationship between theory and practice that comes out of the development of our work as researchers and mathematics teacher educators. The article presents the different steps we have identified in the relationship between theory and practice during our professional development. In the discussion, we examine the whole sequence of steps showing what we have learnt. Afterwards, we use the sequence of activity of the reflective process as a framework in which we can operate and reflect about our own development.