This article is a conversation-analytic investigation of the forms of organization that allow specific items of classroom discourse -words, phrases, up to whole turns at talk -to be altered by subsequent items. Central to the article is an analytic distinction between self-correction and other-correction, that is, between repair sequences in which the speaker of the initial item (the "trouble source") makes the correction and instances in which this is performed by one of her or his interlocutors (cf. Jefferson 1974; Schegloff et al. I977). The classroom case is analytically interesting both for its own sake and also on account of research speculations that other-correction should be more frequent in adult-child talk than in other genres of conversation. However, in order to provide an analysis of the problem sensitive to the particularities of the classroom, it is necessary to look not merely at corrections, but at the larger repair trajectories in which they occur. These trajectories consist of corrections plus their prior initiations, the latter being means by which speakers mark out some item as requiring correction. Once the social identities of teacher and student are mapped against selfand other-forms of initiation and correction, it is possible to discern some of the structural preferences of classroom discourse along the general axis of repair.