There is increasing acknowledgement of mentoring as a form of professional development with the potential to benefit both individuals and organizations. In Singapore, mentoring was the main feature of a development strategy for aspiring school principals attending the Diploma in Educational Administration (DEA) programme at the National Institute of Education (NIE) of the Nanyang Technological University. It was developed as part of the DEA programme since 1984. Sustained over a period of more than one-and-a-half decades, the Singapore model was one of the longest established formal mentoring schemes for aspiring principals. As such, it offers a rich setting and background for research on mentoring. Mentoring literature on headteachers may focus on significant aspects such as "what was discussed" and "what was learned", but is silent about the actual consequent practice of such learning in the workplace. This article presents part of a bigger study which was carried out to explore the practice of school management learned, as perceived by secondary school principals who have the opportunity to learn through mentoring. The focus was on what could be learned in a formal mentoring programme and what could be put into practice on the job.