This paper is concerned with the process of how subject and pedagogic knowledge emerge through teachers' learning in science. It suggests that problematizing subject knowledge through direct experience of learning in science, particularly in those areas that are known to be difficult, constitutes a productive way of turning a deficit model of teacher subject knowledge into a positive experience with considerable potential for the development of pedagogy. The paper draws on exemplification of student learning to contextualize the discussion within current debate in science education concerned with conceptual change and metacognition. It is argued that the act of addressing what are problematic science concepts in their own learning, affords an opportunity for students to focus on the nature of the concepts being explored and how understanding of them might be developed. It is implied that a notion of "learning practice" in university taught sessions, in addition to the embedded model of generating pedagogic insight through teaching experience in school placements, would constitute a productive mechanism for the synthesis of subject and pedagogic knowledge. (Contains 2 figures.)