This paper reports on teachers developing their own data literacy and then acting as data coaches for colleagues in their schools. The 13 teachers from 7 schools in the study analysed standardised data using a data conversation protocol to identify students with significant mathematical misconceptions. They then took data-informed action with these students. Through this inquiry process, they developed confidence to act as data coaches with a small number of colleagues. By positioning themselves as co-learners with those they coached (coachees), the teacher-coaches circumvented school power dynamics. Instead, they drew authority from their own inquiries using the data conversation protocol. Nonetheless, some faced challenges when coachees were assigned to the process and/or the formative intent of data use was not clear to coachees.