If there is one finding on which students of classroom discourse are agreed, it must be the ubiquity of the three-part exchange structure that Lemke (1985, 1990) calls “triadic dialogue.” In its prototypical form, this discourse format consists of three moves: an initiation, usually in the form of a teacher question, a response, in which a student attempts to answer the question, and a follow-up move, in which the teacher provides some form of feedback to the student's response. Actual frequencies of occurrence vary considerably, of course, but in many secondary classrooms it is estimated that this format accounts for some 70 percent of all the discourse that takes place between teacher and students, and even in some primary classrooms it has been found to be the dominant mode in which the teacher converses, even when talking with individual students.

When it comes to evaluating the educational significance of this mode of classroom discourse, on the other hand, there is much less agreement. Sinclair and Coulthard (1975), for example, seem to assume that triadic dialogue simply is the unmarked mode of classroom interaction: Unless there is a good reason to behave otherwise, teachers adopt this mode by default. Not surprisingly, therefore, they offer no evaluation of its educational effectiveness. Others, by contrast, while accepting its pervasiveness, claim that it is, in fact, functionally effective. Mercer (1992), for example, argues that triadic dialogue is justified as an effective means of: “monitoring children's knowledge and understanding,” “guiding their learning,” and “marking knowledge and experience which is considered educationally significant or valuable.”