A major implication in the communicative approach to the teaching of foreign languages concerns classroom interaction in which students should participate. Ideally, this interaction should be identical to interaction in real-life communication situations that students will encounter. A prerequisite for determining whether these situations are in fact being used as a basis for second language teaching is a rigorous and explicit model of verbal interaction. This article presents such a model. The model is applied to the description of a portion of classroom interaction. This application reveals that what goes on in classrooms is far from the goal of realistic interaction. Some suggestions for teaching methodology are made. (CLK)