Within-class ability grouping (WCAG) is widely used in elementary mathematics instruction in the United States, yet it has drawn criticism on the grounds that it can inequitably limit the learning opportunities of some students, not least because of its connection to between-class ability grouping (BCAG) that is more common in middle or secondary schooling. Meanwhile, some high achieving countries use relatively little ability grouping in elementary school in comparison to the United States. In this paper, we draw on qualitative data from a series of assignments in four sections of an elementary mathematics methods course in the beginning teacher education programme at a United States university. These assignments were designed to explore the potential of using preservice teachers' (PSTs') memories of and experiences with ability grouping in their own schooling to support critical reflection about the possible negative consequences of within-class ability grouping practices. We found that while many PSTs reported negative personal experiences with ability grouping in mathematics, they often remained uncritical when reflecting on the use of ability grouping in the elementary classes they visited as part of their teacher education programme.