The fact that the spoken texts of classroom interaction - particularly those involving the teacher with the whole class - are co-constructed relatively smoothly, despite the number of participants involved, suggests that they are organized in terms of standard strategies, embodied in typical forms of discourse that have evolved for responding to recurring types of rhetorical situation (Miller 1984; Kamberelis 1995). That is to say that, like written texts, they can be thought of as being constructed according to one of a set of educational genre specifications. One such rhetorical structure, the ubiquitous 'triadic dialogue' (Lemke 1990), also known as the IRE or IRF sequence (Mehan 1979; Sinclair and Coulthard 1975). It has attracted considerable attention in recent years, and has variously been seen as, on the one hand, essential for the co-construction of cultural knowledge (Heap 1985; Newman et al. 1989) and, on the other, as antithetical to the educational goal of encouraging students' intellectual-discursive initiative and creativity (Lemke 1990; Wood 1992). Drawing on episodes of teacher-whole-class interaction collected during a collaborative action research project, this paper will show, however, that the same basic IRF structure can take a variety of forms and be recruited by teachers for a wide variety of functions, depending on the goal of the activity that the discourse serves to mediate and, in particular, on the use that is made of the follow-up move.