Background/purpose: This study explores the different ways in which critical friend roles are conceptualized. The critical friend role is adaptive by nature, with significant ambiguity surrounding it, which has resulted in disjointed and fragmented literature. This study sought to provide insights into the varied and potentially boundary-spanning roles that critical friends may need to draw upon when supporting school-based improvement work. Materials/methods: A focus group methodology was adopted to examine the type of role that experienced critical friends anticipated that they would be required to undertake as part of a longitudinal school improvement program. A semi-structured interview protocol guide was used to uncover the participants' prior experiences when undertaking the role of a critical friend. Results: This study analyzed the work of five critical friends whose primary role was to support principals to lead improvement in improving teaching and learning in mathematics. The results show that critical friends defined four key archetypes they anticipated to utilize during the professional learning program. Conclusion: The study highlighted that the role of the critical friend in supporting improvement is quite varied. The critical friend role can differ depending on the context, level of trust in the relationship, and the core work that is to be undertaken.