Although a wealth of research has been conducted on the educational and broader outcomes of sorting students in different educational tracks (ability grouping) in secondary schools (in Flanders: ASO, TSO and BSO), there is virtually no research that investigates how young people develop ‘track identities’ in such contexts and how such identities in turn relate to particular educational outcomes. This study uses data from the large-scale quantitative FWO funded SIS project (School, Identity and Society) to investigate the development and influence of students’ track identities in Belgian secondary schools (Brussels, Flanders and Wallonia). Building on social psychological theories of in-out group relationships, ethnic identity theory and educational research on tracking, this study investigates how particular dimensions of students’ track identities (such as the private and public regard of these identities), relate to school structural features (within and between school tracking, friendship ties) and teachers’ views about such tracks as communicated to students, and how particular dimensions of track identities in turn relate to students’ sense of futility and their self-esteem.