In this article, Mason's 'discipline of noticing' is used to theorise a reflective process for changing mathematics teaching in a challenging context. The methodological approach was guided by critical reflective processes that produced, firstly, a descriptive 'account-of' an unsuccessful mathematics lesson, followed by layers of analyses drawing on theory and literature that guided our development of 'accounts-for' the classroom interactions. This example of a South African teacher-researcher's self-study on disruptive learner behaviour in her Foundation Phase mathematics class is useful at the practitioner level, in which it details how increasingly critical layers of pedagogic reflection can be used to transform mathematics teaching, and via this route, to improve access to mathematical learning in a challenging context. At the research and policy levels, our findings question the separation of attention to mathematics and learner behaviour, rather than addressing the two in combination.