Reflective practice is an important vehicle for the apprenticeship of tacit and procedure-oriented knowledge. This article explores the development of reflective practice in the teaching of an innovative design course. Starting from a characterization of the "materials of a design situation" (problem-solution duality, methods and tools, management, piloting and organization of projects), we analyse the contributions brought to this practice based on the results obtained within a Masters Degree course. Reflective practice contributes at least two issues: the conscious use of tools in design process and the acquisition of keys to self-analyse the individual and group position and to understand and to manage project uncertainty. (Contains 2 figures.)