Within the overall STTIS (Science Teacher Training in an Information Society) framework, this paper focuses on transformations of innovative teaching of optics, following a recommended change of approach to optics in the French curriculum. The empirical investigation of how teachers responded to this change, the main results of which are briefly presented here, identified a crucial aspect of the problem. This is the importance of "critical detail": that is, the fact that the linkage between certain critical details of practice and the fundamental rationale of a teaching sequence is often not easily understood by teachers, even those who are strongly motivated. The paper then discusses the development of guidelines for the design of training materials based on these research findings, which show how teachers typically tend to transform innovations when putting them into practice. We describe the rationale behind and structure of some teacher training materials intended to facilitate awareness and mastery in this respect.