<p>This paper explores the research mentoring practices of experienced mentors within the Goethe-Institut’s continuing professional development (CPD) programme for teaching German as a foreign language “Deutsch Lehren Lernen”. The CPD includes a research-based learning project in each module called a “Praxiserkundungsprojekt” (PEP). Within each PEP, teachers engage in research into their own practice, with experienced teacher-mentors supporting them. Based on the qualitative analysis of 17 in-depth interviews with expert teacher-mentors from all over the world, the paper offers 11 salient practices for mentoring in-service research-based learning as a form of teacher education and training. We propose that this approach is potentially transferable to adult education contexts in general, and other practice based training contexts in which novice practitioners are actively engaged in research. A new mentor-specific practice from the narrative accounts in this context contributes to our understanding of the mutual benefits from working in a mentor-mentee relationship during research-based learning. It acknowledges the benefit of self-reflection for the mentor – contributing further to the continuing professional development of all involved. This is described as a form of professionalisation in mentoring within teacher training contexts: a form of reflection in action that mentors can model in their mentoring practice (by explicitly reflecting on their own teaching practice as a form of role modelling for the benefit of the teacher-researchers). The demonstration of commitment to reflective practice was unanimously demonstrated by the interviewees, who used this value position to underpin their mentoring.</p>