In order to support professional development of their teachers 14 Dutch secondary schools developed and implemented a series of interventions. The concept of School as Professional Learning Community was used to frame these school interventions. Data were collected through project documents, interviews with school principals and project leaders, group interviews with teachers and focus groups with project leaders. Interventions can be grouped into five clusters: 1) Shared school vision on learning; 2) Professional learning opportunities for all staff; 3) Collaborative work and learning; 4) Change of school organisation, and 5) Learning leadership. Interventions aimed at teacher-leaders, team leaders and school principals were relatively rare. Interventions belonging to the clusters Professional learning opportunities and Collaborative work and learning were the ones most frequently mentioned including formal and informal teacher groups working and learning together. In general, we conclude that the more embedded an intervention was in the organisation and culture of a school, the more sustainable it appeared to be.