Kerr, N. L., & MacCoun, R. J. (1984). Sex composition of groups and member motivation: Effects of relative member ability. Journal of Basic and Applied Social Psychology, 5, 255-271.

Examined the effects of group members' relative task ability on the relationship between group sex composition and member task motivation. 61 male and 61 female undergraduates performed a simple motor task with an opposite-sex partner, a same-sex partner, or no partner. Partners had higher, equal, or lower task ability than Ss. When the partner was more able than the S, both sexes did more work with an opposite-sex partner than when working individually, whereas Ss with a same-sex partner did no more work than individual controls. Group sex composition did not affect member motivation when the partner was equally or less able. Findings disconfirm several models of the sex composition^motivation relationship. Results support an esteem maintenance model that holds that both sexes place greater value on demonstrating competence to opposite-sex partners than to same-sex partners.