There is a growing body of action research on school improvement and development. Many of these studies have found the use of critical friendship valuable in relation to teachers’ or principals’ practice. Yet, little attention has been paid to critical friendship at the school district level. This study explores how a superintendent and three principals changed their understandings through interaction with a critical friend. It draws on reflective conversations, written reflections and observations of meetings between the participants, and is framed within practical action research aimed at changing the participants’ understandings. We found that through a trust-building process the critical friend acted as a catalyst for systematic reflections, helping leaders to set aside time and space to reflect. This has contributed to new ways of talking and thinking and has enhanced the leaders’ system thinking.