AbstractIn this article, we report on the work of developing primary school teachers' mathematical knowledge for teaching (MKfT) in research-led ways. We share data of a Grade 2 teacher who participated in a follow-up to an in-service professional development ‘maths for teaching’ course in 2012. The follow-up consisted of a lesson observation and a subsequent video-stimulated recall interview, with reflections guided by the structure of Rowland et al.'s ‘knowledge quartet’. Our findings point to potential for ongoing learning beyond in-service course participation, with a research-led framework supporting the teacher to bring (perhaps) tacit assumptions of prerequisite skills explicitly to the fore. The article concludes with an appraisal of how research can directly feed into design focused on substantive development of MKfT.