Mentoring is acknowledged as an essential prerequisite for successful teacher induction, but its effectiveness may vary depending on the mentor's quality of support and the mentee's initial professional beliefs. Focusing on novice teachers' self-efficacy and emotional management, this longitudinal study investigates how constructivist- and transmission-oriented mentoring approaches support beginning teachers' professional development, and how these approaches interact with the novices' initial beliefs about teaching and learning. The data stem from a sample of 138 beginning teachers who participated in an online survey during their second and third trimesters of practical training in Germany. Moderated regression analyses indicate positive effects of constructivist mentoring on teacher self-efficacy 6 months later, and an enhancing moderation effect of mentees' mismatching, transmissive beliefs. Results neither support distinct effects of constructivist mentoring on novices' emotional management nor associations between transmissive mentoring and the outcomes. Implications for mentoring research and practice are discussed.