Purpose -Executive coaching has become increasingly important for enhancing organizational leaders' professional effectiveness. The purpose of this paper is to contribute to a growing body of research literature that examines how coaching techniques help school principals improve their instructional leadership. Design/methodology/approach -Using a protocol based on a theories of practice framework (Argyris and Schn, 1974) to support principals in deepening their self-reflection, this study added the element of a guided peer-coaching component in a group setting. Findings -Results confirmed the effectiveness of the coaching protocol for assisting principals in deepening their self-awareness and critical reflection regarding their leadership, including the way principals' core assumptions about teaching and leadership shaped the outcomes of their problem-solving strategies. Perceptions of the peer-coaching element were mixed, however. While principals reported feeling affirmed by sharing their leadership challenges with others, and indicated that the group coaching experience contributed to their sense of professional community, there were limitations to principals' willingness to challenge one another's core assumptions. Originality/value -This study builds on literature that cites theories of practice as a mechanism for enhancing professional effectiveness and represents a further iteration of recent research studies applying the concept to the work of school principals. Findings affirm that a coaching protocol based on theories of practice is well received by principals, serves to deepen self-reflection, and can, in limited cases, contribute to sweeping changes of thinking and practice congruent with the concept of double-loop learning.