During 2001-2002 the Faculty of Education at the University of Hong Kong undertook a large-scale evaluation of the school-university partnership scheme. As part of this study, all mentors were asked how, if at all, the mentoring process had enhanced their own professional development. An open-response questionnaire was administered with a selection of follow-up interviews. About 70% of the mentors claimed that they had benefited professionally from mentoring. Here we analyse mentors' responses and from them propose four constructs that we suggest lead to professional development, namely: learning through self-reflection, learning from student teachers, learning through mutual collaboration, and learning from university tutors. Of these, the first appears to be the most significant. [Copyright of Journal of Education for Teaching is the property of Routledge. Full article may be available at the publisher's website: http://dx.doi.org/10.1080/02607470500043532]