Clinical reasoning is the cornerstone to healthcare practice and teaching it appropriately is of utmost importance. Yet there is little formal training for clinical supervisors in supervising this reasoning process. Distance education provides interesting opportunities for continuous professional development of healthcare professionals. This mixed methods study aimed at gaining in-depth understanding about whether and how clinical teachers can develop complex pedagogical competencies through participation in a Massive Open Online Course on the supervision of clinical reasoning (MOOC SCR). Participants self-assed their clinical supervision skills before and after partaking in the MOOC SCR through the Maastricht Clinical Teachers Questionnaire. Item scores and the distribution of response proportions before and after participation were compared using paired t-tests and McNemar’s tests respectively. In parallel, the evolution of a subset of MOOC participants’ pedagogical practice and posture was explored via semi-structured interviews throughout and beyond their MOOC participation using simulated and personal situational recalls. The verbatim were analysed with standard thematic analysis. Quantitative and qualitative findings converged and their integration demonstrated that partaking in the MOOC SCR promoted the development of complex pedagogical competencies and reflexivity with the participants. This was quantitatively evidenced by significantly higher self-assessed supervision skills and corresponding attitudes after completing the MOOC. The qualitative data provided rich descriptions of how this progression in pedagogical practice and posture occurred in the field and how it was shaped by participants’ interaction with the MOOC’s content and their motivations to progress. Our findings provide evidence for the development of pedagogical skills and corresponding attitudes for the supervision of clinical reasoning through participation in the MOOC SCR and contribute to the literature body on the opportunities that distance learning provides for the development of pedagogical competencies. The extent to which the pedagogical underpinnings of the MOOC contributed to these developments remains to be determined.