This paper focuses on patterns of post-apartheid learner migration between schools previously segregated along racial lines. South Africa's shift away from cultural and linguistic isolationism and the ways this has impacted educational arrangements in this country, most particularly in relation to the language of learning and teaching, affects mathematics teaching and learning in complex ways. We focus on how changes in the demographic make-up of some schools have affected the teaching and learning of mathematics by drawing on two case study vignettes in historically different schools. The vignettes are used to illuminate our discussion and to raise key questions requiring further research.