This paper posits that teachers' pedagogical content knowledge in mathematical modelling instruction can be demonstrated in the crafting of action plans and expected teaching and learning moves via their lesson images (Schoenfeld, 1998). It can also be developed when teachers shape appropriate teaching moves in response to students' learning actions. Such adaptive development of teachers' pedagogical content knowledge may in turn be supported by their knowledge of the mathematical modelling process and Ang's (to appear) proposed framework for planning mathematical modelling instruction.