A cohort of senior students attending five New Zealand secondary schools operating a peer mentoring programme were followed for 24 months. The aims of this project were to evaluate their experiences and overall impact of Peer Mentoring on senior students; investigate factors that are associated with and influence growth in positive youth development (PYD) outcomes; and identify characteristics that distinguish returning mentors from other students. This research provides converging evidence that authentic, ongoing peer mentoring experiences can foster PYD gains for NZ youth.