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 8 schools in the study analysed standardised data using a data conversation protocol, identified students with significant mathematical misconceptions and 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 their coachees the teachercoaches 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.