Two meanings of the word "discourse" are distinguished. The first treats discourse as conversation (D1), and the other refers to different ways of understanding (D2). Rather than seeing the two kinds of discourse as different, they are seen as having an important connection, particularly in classroom communication. Examples are drawn from the literature of classroom interaction. It is argued that critical discourse analysis should be applied not only to the teacher's instructional discourse (D2), but also to his various forms of D1, including how systems of meaning are approached, responded to, talked about, and resisted: i.e., the contact zones in which meanings are made and unmade. Contains 13 references. (MSE)