In recent years policy makers' interest in the professional development of school leaders has grown considerably. Although we know some aspect of formal educational programs for school leaders, little is known about school leaders' incidental and non-formal learning in the workplace. This study aims to grasp what workplace learning activities school leaders value most, what work-related questions incite them to learn, what outcomes they achieve through workplace learning and what conditions support workplace learning of school leaders. In order to generate answers to the research questions, we conducted semi-structured interviews with 20 Dutch school leaders in secondary education, which also served as a form of reflection for the respondents. Results show that school leaders mostly value workplace learning through working on improvement and innovation and through reflection. In addition to outcomes for the school leader, working on improvement and innovation also leads to learning outcomes for teachers, and seems to provide opportunities for teachers to influence changes in the school. On the other hand, teachers take little or no part in reflection. Here, school leaders find peace and stability to reflect with fellow school leaders. If adjusted to a specific context, the methods used in this study might be transferred to other contexts, to study workplace learning of all kinds of leaders.