There is widespread belief that addressing differentiation within classroom practice is critical for school improvement in mathematics. School mathematics leaders and consultants are faced with the challenge of interpreting the various models of differentiation that are presented throughout professional learning programs and aligning these with existing beliefs and cultures within schools. This paper reports on a self-study of a learning consultant who supported primary mathematics teachers to plan lessons for implementing differentiation in their classrooms and aims to highlight the Mathematical Knowledge for Teaching (MKT) required to lead such planning sessions. Over three weeks, a mathematics consultant assisted teaching teams across three different schools by facilitating planning meetings. The consultant recorded self-reflections after each session and the qualitative data were coded to identify the categories of MKT the consultant relied on during her interactions with teachers. Overall, the results highlight the dominance of three categories, Knowledge of content and students (KCS), Knowledge of content and teaching (KCT) and Specialised content knowledge (SCK) emphasised by the consultant, as well as the influence different contexts had in developing a shared understanding of differentiated learning in mathematics. The findings have implications for ways in which schools and facilitators develop strategies that comprehensively support teachers to plan suitable differentiated lessons for their students. Furthermore, this study highlights the need to develop greater understanding around models of planning that adequately support teachers to plan effectively for differentiating instruction in mathematics.