This paper describes the development of curriculum design expertise from the perspective of a teacher reflecting on a science lesson. His involvement in the research process resulted in a self-determined professional development strategy. The description comes from data collected through lesson observations and an in-depth stimulated recall discussion to probe and uncover the teacher's understanding of the importance of the curriculum design principles related to his lesson. These data are supplemented with lessons plans studied over several months. Views expressed indicate that the professional development of the teacher was grounded in trust and trust-building that took time. The views also, suggest, amongst other issues, how empowerment evaluation can be used in enabling development in curriculum design.