Given the significant role that academic self-concept plays in students' learning, understanding the psychological processes involved in its formation continues to be an important focus of enquiry. There is strong empirical support for two major models of academic self-concept (ASC) formation: the big-fish-little-pond (BFLP) model and the internal/external frame of reference model (I/E model), models which emphasise the roles of social and dimensional comparisons in ASC development. The present study aimed to contribute to an emerging body of evidence on the validity of a model that integrates the predictions of the BFLP and I/E models into a unified framework. Models were tested in the domains of reading and mathematics using data from a nationally representative sample of 4166 grade 6 students in 220 classes in Ireland. Central predictions of the BFLP and I/E models held when tested in combination. Specifically, individual achievement in one domain had a significant positive effect on self-concept in that domain and a negative effect on self-concept in the other domain. Additionally, class-level achievement in a given domain was negatively related to self-concept in that domain, after accounting for the effect of individual achievement. Findings support the hypothesis that social and dimensional comparisons have effects on the academic self-concepts of primary school children.