PurposeThe study aims to explore the experiences of new school-based mentors in Norway of an online teacher professional development (OTPD) programme in mentoring. The focus was on how the OTPD programme worked out as a boundary artefact to strengthen the coherence between a university and partner schools.Design/methodology/approachConstant comparative analysis was used to examine 21 school-based mentors' experiences and how the programme worked out as an artefact to strengthen the coherence between the teacher and education arenas. The findings were interpreted considering the literature and OTPD and boundary-crossing theories.FindingsThe findings revealed that the OTPD programme served as a boundary artefact. By participating, the new school-based mentors felt part of a community, identifying as teacher educators. Thus, the programme mediated their understanding of their new role as a teacher educator. Two main tensions were found: first, resistance towards online collaboration with school-based mentors across schools and participants that preferred to work locally with their own colleagues and, second, different technologies at the schools and the university disrupting the participants' experiences. Overall, this study emphasised the value of a facilitator from the university supporting the participants' development in the OTPD programme.Originality/valueThis study provides an understanding of teachers' OTPD when at the boundary of becoming school-based mentors and may contribute to enhancing universities' quality of teacher education. This study also highlights the importance of stronger connections between school-based mentors and their university campuses.