<p>Previous research into the knowledge required for teaching has focused primarily on pre-service and in-service teachers' knowledge. What is less researched, however, is the role of the teacher educator in helping pre-service teachers (PSTs) develop the knowledge needed in order to teach mathematics to students. The focus thus shifts from examining school teachers' knowledge for teaching mathematics to school students, to studying teacher educators’ knowledge for teaching teachers. This raises the question of what is the nature of this knowledge as required by teacher educators, and how evident is it in their practice? This paper documents the interactions among two teacher educators and two cohorts of PSTs enrolled in a unit designed to teach mathematics pedagogy to early childhood and primary PSTs. Over one semester, two teacher educators observed each other’s classes, engaged in reflective professional conversations, and surveyed PSTs about lesson material and delivery. The results indicated there were a number of issues faced by the teacher educators that could be interpreted through the use of a teacher knowledge framework, with examples for this study focussing on a representative lesson. The findings add to the field of research into teacher educator knowledge and have implications for mathematics teacher educators and the pre-service teachers they teach.</p>