Background: Teachers play a critical role in promoting interactions between students and engaging them in the learning process. This study builds on a study by Hertz-Lazarowitz and Shachar (1990) who found that during cooperative learning teachers' verbal behaviours were more helpful to and encouraging of their students' efforts while during whole-class instruction, their verbal behaviours tended to be more authoritarian, rigid, and impersonal. Aim: This study seeks to determine if teachers who implement cooperative learning engage in more facilitative learning interactions with their students than teachers who implement group work only. The study also seeks to determine if students in the cooperative groups model their teachers' behaviours and engage in more positive helping interactions with each other than their peers in the group work groups. Samples: The study involved 26 teachers and 303 students in Grades 8 to 10 from 4 large high schools in Brisbane, Australia. Methods: All teachers agreed to establish cooperative, small-group activities in their classrooms for a unit of work (4 to 6 weeks) once a term for 3 school terms. The teachers were audiotaped twice during these lessons and samples of the students' language, as they worked in their groups, were also collected at the same time. Results: The results show that teachers who implement cooperative learning in their classrooms engage in more mediated-learning interactions and make fewer disciplinary comments than teachers who implement group work only. Furthermore, the students model many of these interactions in their groups. Conclusions: The study shows that when teachers implement cooperative learning, their verbal behaviour is affected by the organizational structure of the classroom.