As investment increases, policy makers are increasingly seeking evidence of the effects of mentoring on teachers' classroom practices and students' learning outcomes. Major funds are allocated to train experienced teachers to become mentors and to then release them from teaching so they can meet with mentees. Large scale longitudinal studies with the capacity to assess the effects of mentoring and its presumed links with changes in teacher knowledge, classroom practices and student outcomes over time are needed. However, different conceptualisations of the term 'mentoring' have made it very difficult to evaluate and compare the outcomes of school mentoring programs (Spooner-Lane, 2016). In addition, studies measuring the effectiveness of mentoring typically lack a strong theoretical underpinning and typically focus on roles, procedures and functions of mentoring (Nahmad-Williams & Taylor, 2015). In the current study mentoring is positioned as an interpersonal relationship for professional support based on a process of collaborative inquiry and critically reflexive praxis. Using a theoretical derived model of dialogic mentoring, the purpose of this study is to develop a new measure to assess the outcomes of mentoring in schools. Given the importance of evidence-based interventions in informing policy and allocation of resources, it was determined that the development of a new measure that evaluates the impact of reflexive professional dialogues was timely. The Dialogic Mentoring Scale will be investigated for its psychometric soundness before discussing implications for future research.