This study identifies and analyses professional norms as a means of illuminating school cultures and how norms are distributed in the system. Of special interest is the role of school leaders and how they lead, organize and realise school development. The study research question is: What professional norms do school leaders highlight in change efforts? We are also interested in identifying the support mechanisms and obstacles to implementation and norm setting exhibited by school organisations. The case we used explores change processes in the implementation of education for sustainable development at three upper secondary schools in Sweden. It was conducted in three phases, starting with a questionnaire for all teachers and principals. In the second phase, each of the principals was interviewed individually. The third phase used focus groups consisting of the principals that made up the leadership groups. Our results indicate that professional norms are set when principals and teachers experience expectations from each other, from students and from policy documents. There is also a need for well-functioning communication in the organisation to set and disseminate norms. The school principal plays a crucial role in these norm setting processes. By becoming more aware of existing norms in the organisations, and how norms can be changed, this knowledge can support principals in change efforts.