This is a position paper in which we argue for "Teaching for Mathematising" as a pedagogy that supports teaching mathematics for understanding in primary school. Mathematics education in Australia currently emphasises teaching for mathematical understanding, a shift that redirects children's learning from merely memorising computation procedures to helping children construct knowledge of the mathematics that informs mathematical "concept and processes." The shift to teaching for understanding however is not reflected in students' item responses in international and national achievement studies. This paper provides one example that illustrates a learning trajectory for supporting mathematical understanding of both conceptual and procedural knowledge through teaching that builds on the framework of "Teaching for Mathematising." A corresponding field-test will then be used to illustrated how students learn pragmatically.