In some forms of practice-based teacher education, one important task for the teacher educator is to undertake in-the-moment coaching during rehearsals of practice. However, being such a coach is a new role for many teacher educators and requires a different skill set to other forms of teacher educator practice. In addition, there is little literature to which teacher educators can turn when seeking to address the problem of enactment in this context. This article seeks to address this gap in the literature. It reports a self-study undertaken by one mathematics teacher educator as he learned to coach pre-service teachers on the fly, while in turn they learned to orchestrate whole-class mathematical discussions. It seeks to illustrate how the process of journaling can support the journey of discovery that is the development of new practice. Through consulting the literature and story-telling, a picture is painted of how the educator addressed early concerns such as "what is a coach supposed to do?" and "what should a coach pause a rehearsal to talk about?" and began to master coaching--work that was never routine, but rather situated, adaptive, and responsive. The stories draw from a personal journal of field notes and reflections from such events as student rehearsals, lesson conferences, team meetings, reading student work, and professional reading. Journal entries from 12 rehearsal cycles over four years were consulted.