Previous research on small-group collaboration identifies several behaviors that significantly predict student learning. These reports focus on student behavior to understand why, for example, large numbers of students are unsuccessful in obtaining explanations or applying help received, leaving unexplored the role that teachers play in influencing small-group interaction. We examined the impact of teacher discourse on the behavior and achievement of students in the context of a semester-long program of cooperative learning in four middle school mathematics classrooms. We conclude that student behavior largely mirrored the discourse modeled by and the expectations communicated by teachers. Teachers tended to give unlabeled calculations, procedures, or answers instead of labeled explanations. Teachers often instructed using a recitation approach in which they assumed primary responsibility for solving the problem, having students only provide answers to discrete steps. Finally, teachers rarely encouraged students to verbalize their thinking or to ask questions. Students adopting the role of help-giver showed behavior very similar to that of the teacher: doing most of the work, providing mostly low-level help, and infrequently monitoring other students? level of understanding. The relatively passive behavior of students needing help corresponded to expectations communicated by the teacher about the learner as a fairly passive recipient of the teacher's transmitted knowledge. Finally, we confirmed previous analyses showing that the level of help received from the student or teacher, and the level of student follow-up behavior after receiving help significantly predicted student learning outcomes.