Seven and 9-year-old children (n=120) worked in same or mixed gender pairs on a language-based computer and non-computer task, and their styles of social interaction were compared. At both ages, mixed gender pairs showed more assertive and less transactive (collaborative) interaction than same gender pairs on both tasks. When collaboration broke down, boys on the computer task and girls on the non-computer task dominated assertive interaction in mixed gender pairs, whereas in same gender pairs both children were equally assertive. The mediational role of the computer and the social dynamics that frame its use are discussed.