Peer mentoring is becoming increasingly popular in UK higher education, however, there remains little good quality, theoretically driven and evaluative research. The current study aims to bridge the gap between theory, practice and evaluation by providing a controlled evaluation of a peer mentoring scheme within UK universities. 109 first year undergraduates from two matched universities completed questionnaires at two time points: during the first week of university and again 10 weeks later. Results focused on direct, mediating and moderating effects of mentoring on levels of wellbeing, integration and retention. Peer mentored individuals showed higher levels of integration to university. Four times as many non-peer mentored students had seriously considered leaving university compared to peer mentored students. Integration partially mediated the relationship between mentoring and intention to stay at university. Moderating effects analyses indicate that mentoring may buffer the effect of the transition to University. Results are discussed in relation to Tinto's theory of student retention, the benefits and practicalities of peer mentoring within UK universities and the methodological limitations within this study.