This study investigated the comparative effects of audio-visually prompted collaborative dialogue on the listening comprehension development of symmetrical, asymmetrical, and asymmetrical teacher-fronted EFL learner groups. Besides, it explored the attitude of the participants of the groups concerning the effectiveness of collaborative dialogue for their listening comprehension improvement. The participants of the study were 120 Iranian female EFL learners who were conveniently chosen from several English language institutes and put into three experimental and one control groups, each with 30 learners. In the first experimental group, coequal learners engaged in collaborative dialogue. In the second experimental group, the expert peer(s) and less knowledgeable peers applied collaborative dialogue, and in the third experimental group, in addition to the peers, the teacher was involved in collaborative dialogue with the group members. As for the control group, the collaborative dialogue was abandoned and the participants worked individually. Quantitative and qualitative analyses revealed that collaborative dialogue in asymmetrical teacher-fronted, asymmetrical peer and symmetrical peer groups were respectively the most effective procedures for listening comprehension development of the EFL learners. Also, it was found that the participants of the asymmetrical teacher fronted group had a more positive attitude towards the efficacy of audio-visually prompted collaborative dialogue compared with asymmetrical and symmetrical peer groups. The findings underscore the cognitive and affective efficiency of a more knowledgeable source, either a teacher or a peer, in asymmetrical dyadic interactions for the less knowledgeable partners' ZPD sensitive development.
