The goal of this article is to report on the challenges the authors faced in designing an instrument aimed at measuring pre-service science teachers’ topic-specific pedagogical content knowledge (PCK(. The discussion focuses on the implications of the aforementioned PCK assessment tool for enhancing pre-service science teachers’ topic-specific PCK and the challenges associated with measuring and enhancing pre-service science teachers’ PCK. Furthermore, the discussion focuses on the ways in which science-teacher educators can engage in transforming the concept of PCK and its use for research and professional development.