In this paper the relationship of identity to a form of institutional interaction is considered, i.e. classroom talk. To illustrate this relationship and its variations, applied ethnomethodology was used to explore the issue of the behavioural and interactional latitudes that the participants afford one another. To do this, features of the assembly and coordination of identities for and in two classroom lessons were compared. The results illustrate ways in which the institutional identities of teacher and student are enacted through and in the interactions in classrooms. It is proposed that, even when such powerful categorizations as ethnicity, class and gender are readily available as potential organizers of practical events such as these lessons, the analysis needs to begin with the empirical structure of the events themselves, treating them as displays of coordinated reasoning practices, and thus treating the contingently assembled identities of the participants as social, locally activated, and resolutely practical.