Like any other complex agenda of reform, the notion of teaching for understanding contains areas of uncertainty and ambiguity. This paper uses an hermeneutic research cycle to identify some uncertainties in understanding of teaching for understanding. These areas of uncertainty are discussed in relation to the literature and vignettes from three interpretive case studies of science teaching. Three questions are considered: Is teaching for understanding a method or an outcome of teaching? Does specialist language interfere with understanding, or construct it? What kind of understanding does teaching with analogies promote? It concludes with a discussion of four issues: the difficulties faced by teachers in teaching for understanding, the wider context of school science, the nature of teacher change, and the need for elaborated examples of successful teaching for understanding.