If research and development in the field of learning design is to have a serious and sustained impact on education, then technological innovation needs to be accompanied--and probably guided--by good empirical studies of the design practices and design thinking of those who develop these innovations. This article synthesises two related lines of research into teachers' design thinking. We draw attention to the importance of context in working on the solution of design problems and introduce the idea that some pedagogical knowledge can best be understood as "knowledge in pieces", rather than as a coherent system of pedagogical beliefs. (Contains 1 figure and 2 tables.)