Social constructivists have made continuous calls for more collaborative group work within primary pedagogy. They claim that such an organisational strategy will enable children to use talk to help them make meaning, and enhance their critical and creative thinking. It is widely acknowledged that organisation of children in groups has become a common device in primary schools; however, there is little evidence to suggest that children are working collaboratively. This paper presents classroom data of group work in practice. It is drawn from ten years' experience of collaboration between a classroom teacher and researcher. The findings support the view that collaborative learning tasks need careful planning of both the task and the classroom organisation. It is argued that the composition of collaborative groups should be careful planned to take account of the social contexts in which group work takes place. Transcripts of children's talk are analysed to see how the composition of the groups, the task set, and the classroom organisational strategies can contribute to successful group collaboration.