The present study sought to compare the effects of training teachers in specific communication skills designed to promote thinking and scaffold learning on teachers' and students' verbal behaviours during cooperative group work. Thirty teachers and 826 children from years 5 to 7 participated in the study. The results show that when teachers are trained to use specific communication skills during cooperative learning (cooperative-interactional condition) they engage in more mediated-learning interactions, ask more questions, and make fewer disciplinary comments than teachers who have been trained to implement cooperative group work only (cooperative condition). In turn, the children in the cooperative-interactional groups modelled many of the responses they gave their teachers and provided more detailed explanations, shorter responses, and asked more questions than their peers in the cooperative only groups.