Continuing professional development approaches such as professional learning communities (PLCs) could help schools to sustainably work on school improvement to meet the rapid changes in the world around us. Sustainability is achieved when the core components of the approach become a self-evident and functional part of the school (or: organizational routine), which is flexible and adaptive to ongoing work, and aimed at regular improvement.

Achieving sustainability has been found to be a challenge for a lot of schools, however. Leadership is assumed to be crucial for sustainability. We studied leadership through a distributed leadership lens: all activities tied to the core work of the school that are designed by the school’s staff members to influence the motivation, knowledge, or practices of other members of the school organization were considered.

As research into sustainability of professional development and leadership was scarce, this dissertation focused on the following question: What is the role of school leadership in schools that work sustainably on school improvement with PLCs? A case study design was used to gain in-depth insight into what leadership and sustainably working on school improvement with PLCs looks like in five Dutch secondary schools. The schools were intensively observed (approximately 160 hours per school), school (policy) documents were collected, social network questionnaires were administered, and the school leadership was interviewed.

Based on four studies, that focused on leaders’ practices, knowledge brokerage, and beliefs, the role of school leadership appears to be threefold. They 1) adequately designed the organization for working with the PLC, 2) managed the teaching and learning program while considering the PLC, and 3) helped and supported the staff members’ development for working with the PLC. The way in which leaders carried out the triple role of leadership seemed to be related to different factors. These factors are situated at the personal, interpersonal, and school contextual levels. The dissertation shows what leadership practices were carried out in what way and provides practical implications resulting from that. The insights could inspire schools and school leadership to work sustainably on school improvement with PLCs too.