The purpose of this study is to examine whether quality and frequency of mentoring predict beginning teachers’ development of professional competence and well-being in the first two years of their career. Findings indicate that the quality of mentoring rather than its frequency explains a successful career start. Additionally, beginning teachers who experience constructivist mentoring show higher levels of efficacy, teaching enthusiasm, and job satisfaction. Constructivist mentoring also reduces emotional exhaustion after one year of training compared to teachers without constructivist mentoring.