Mentor teachers have a prominent role in teacher education as they work in close cooperation with student teachers during their work-based education. Research has shown that mentor teachers rarely focus on student teachers’ coping strategies (Heikonen et al., 2017) and issues related to power imbalances (Lilach, 2020), which in turn may impede the relationship between the mentor and student teacher. Nonetheless, when the relationship between them is set on cooperation, there are numerous studies pointing to the importance of the mentor teacher.  This study aims to explore the mentor teachers’ perspectives on having challenges creating positive relationships with student teachers. In this process, mentor teachers judge the student teacher’s suitability for working as a teacher in both a formal and informal manner. Thus, we explore mentor teachers’ meaning-making of how they approach student teachers if they judge that they are not making any progression during the work-based education.  We adopted symbolic interactionism and constructivist grounded theory as a theory-methods package (Charmaz, 2014). GT is a flexible, systematic and iterative approach from which we used coding, memo-writing and constant comparison to guide data collection and analyse the data.  The study builds from two sets of interviews, exploring the emergent categories of suitability and distance in these interviews. In total, 25 mentor teachers were interviewed during the first interview, and after approximately seven months 22 of the mentor teachers were interviewed again. The findings show that mentor teachers engaged in a suitability judgment of their student teachers that focused on (1) compliance of the student teacher to school-based norms, and (2) how they perceived that student teachers engaged in using their experiences to progress. This suitability judgment was used to develop actions meant for the student teacher to use in developing their practice as teachers. A reported concern was when mentor teachers perceived that student teachers did not follow their instructions and thus, according to the mentor teachers, did not progress. This lack of progression was found in relation to student teachers’ teaching and ability to act socially with pupils and colleagues.  This study is relevant to Nordic Educational Research since it addresses mentors’ perspectives on establishing co-operative relationships with student teachers. We hope this might be of use in the discussion about ways to support mentor teachers when they face problematic situations with student teachers.