- Pedagogical content knowledge,
- Mathematical knowledge for teaching,
- Reflected abstraction,
- Psychologizing the subject matter
In this theoretical paper, I review the history of research in educational psychology that inspired Shulman’s notion of pedagogical content knowledge (PCK) and critically examine interpretations of PCK reflected in prominent theoretical frameworks for mathematical knowledge for teaching (MKT). I propose a theory of PCK—grounded in radical constructivism, Piaget’s genetic epistemology, and empirical research results—that addresses limitations of these prominent frameworks. I conclude with a description of what makes PCK in the proposed theory “pedagogical” and describe a research agenda that reconnects MKT scholarship to its Deweyan philosophical foundations.