Mentoring is a favoured practice in many fields, including teacher education. This article challenges the uncritical acceptance of the beneficial effects of mentoring, by developing a novel conceptual model which allows to theorise and study mentoring as a discursive practice, focusing on the relations between all actors involved (i.e. teacher educator, student teacher, mentor), located in broader socio-cultural contexts. The model integrates (elements of) positioning theory and frame analysis which together deliver the necessary conceptual tools to explain how mentoring triads exactly operate and why they operate as they do. The model is substantiated with empirical results from an exploratory single case-study of one mentoring triad from a teacher education provider in England. The article concludes with an agenda for future research, inviting the research community to engage with the proposed model to start building a broader evidence base in both the dynamics and outcomes (broadly defined) of mentoring.