Previous research has demonstrated the cognitive and affective benefits to be accrued from co‐operative group work. However this body of research has largely been limited to consideration of group products rather than group processes and as such has failed to provide explanations of how, or why, improved outcomes occur.This study focused on group processes in order to throw light on the relationship between group composition, interactive processes and pupil understanding on a cooperative decision‐making task. More specifically it reports on the nature and type of talk in homogeneous, heterogeneous and mixed attaining groups, and their relationships to pupil retention and understand