Based on data drawn from an empirical research project in four UK universities, this article presents a picture of student positions in undergraduate classes as a product of the relationship between the discursive fields of discipline, institution and gender. It begins by providing a description of some contrasting features of academic disciplines, and then identifies ways in which these features conflict with features of other discursive fields, to marginalise specific students or groups of students. The article draws on the conceptual vocabulary of Ernesto Laclau and Chantal Mouffe to argue that where features of discursive fields overlap, social identities are overdetermined, while where features of discursive fields conflict, social identities are placed in an antagonistic and unstable relation to social and symbolic systems.