Background: This article casts the analytical spotlight on the practice of within-class homogeneous (same) ability grouping where learners are placed in small groups for instruction based on their perceived performances, reading levels and interest. Very few studies have focused on within-class ability grouping, especially in a South African context, where this homogeneous style within-class grouping is the dominant practice in Grade 1 classrooms, despite literature's cautions against its continuous use. Aim: This article aims to address the following questions: what are the manifestations of the practice of within-class homogeneous ability grouping, and how does it account for learner achievement levels in Grade 1 classrooms? Setting: A total of 12 Grade 1 learners, in relation to their teachers and their principals, from three selected public schools in the Western Cape, were interviewed and observed within a classroom setting. Bourdieu's work is used to explain the interiority and exteriority of social relations, how practice gets internalised and embodied on the inside, and manifested in various ways on the outside. Methods: This empirical exploration used the qualitative-interpretive paradigm and followed a multiple case study approach where 6-year-old Grade 1 learners were observed and analysed. Results: The results show differential treatment of groups and the labelling of learners, which gets internalised constituting particular learner dispositions and resulting in learner agency. Furthermore, it shows how learner agency is being informed and constituted in ways that affect their educational outcomes in profound ways. Conclusion: The author argues that by placing children in groups based on their perceived ability results in the children gaining differential learner experiences and ultimately attaining differential learner achievement levels. In other words, it creates differential environments within the same classroom enabling some to outshine while disabling others.