This evaluation used a change transition model to explore the processes of development of a three-phase professional programme devised by two teams of researchers to support teachers' expertise in six domains of science teaching. The full programme operated over two years. Interviews with developers at the end of each phase (21 interviews) and with teachers at the end of phases two and three (11 interviews) formed the main data set. The four features of the change transition model--trigger, vision, conversion, maintenance--were used as a framework for analysis of the qualitative data. Four themes emerged as contributing to the success of the process of development of the programme: establishing a shared vision of the goals of the programme and its outcomes; maintaining flexibility in implementing the phases and details of the programme; negotiating common understanding with participants; and ensuring fruitful collaboration in planning and implementation. The demands of attending to all of these features should not be underestimated in any successful developmental process. The evaluation therefore provides evidence for additional guidance in future collaborative professional development.