Introduction: Reflective competence is fundamental for responsible medical practice and must be systematically incorporated in medical training. To promote this, a longitudinal portfolio-based mentoring program was made mandatory at the Medical Faculty of the University of Tübingen in 2013. This study examines medical students' attitudes toward professional reflection and toward the program in general to draw conclusions about conditions as well as the needs-based design of the program. Method: In winter semester 2017/18, a retrospective questionnaire survey with free text fields was conducted (total sample: N=1.405; students S 1-9; response 37%; S 1-4 “Pre-clinic”: n=231; S 5-9 “Clinic”: n=241). Opinion trends of semester groups were identified through seven semi-structured interviews with semester speaker and peer tutors. Results: Differences in understanding and attitudes resulted in three positions: 1=approval, 2=ambivalence, 3=rejection. All three groups included individuals from pre-clinical and clinical settings with varying levels of experience. Prior experience and hidden curriculum influenced the position. Opinion trends confirmed the feedback. Conclusion: Although reflection appears in the National Competence-based Learning Objectives Catalogue for Medicine (NKLM), reflective competence is not regarded as equivalent to other study content. Motivation, commitment on the part of the mentors, and a trusting mentor-mentee relationship are effective. The flexibility of the portfolio in terms of content and methodology, as well as the curricular integration of the program are also beneficial.