Mentoring of pre-service teachers in their school practicum is vital to integrating different parts of the educational programmes and supporting the pre-service teachers to become educational professionals, but for mentors in schools this task often comes on top of the other requirements they face as teachers. In this study, we present findings from a self-report survey completed by 295 mentors in two teacher education institutions in Norway. Using structural equation modelling of cross-sectional survey data, the study explores predictions of the effort mentors put into their work in supporting the development of pre-service teachers. The findings indicate that affective commitment predicts mentor's efforts in mentoring and that professional development of mentors through programs designed to develop a professional identity as mentors could enhance their feeling of being teacher educators, and thereby having the willingness to put effort into their jobs as mentors.