Gender and ethnicity are important aspects of children's everyday social relationships, yet little is known about how these social categories influence children's collaborative interactions. In the present study, 322 White (Caucasian) and South Asian boys and girls (mean age, 7.5 years) collaborated in pairs on easy and difficult versions of a model completion task. As expected, girls were less assertive than boys in conversation, yet this relation held only for all-Asian pairs (i.e., an Asian boy and girl in conversation). Also consistent with expectations, levels of conversational affiliation were lowest in cross-ethnic interaction. The influence of gender and ethnicity on conversations did not vary in light of contrasting cognitive demands of the tasks. Results are discussed in relation to work on effective peer collaboration and the potential role of contact in promoting positive ethnic and gender group attitudes.