White American-Caucasian children from 6-12 yr showed significant sex differences on four tasks of rapid automatized naming; and in each case, girls outperformed boys. American-Chinese, native Japanese and native Korean schoolchildren did not differ from American-Caucasians in naming speed when scores for boys and girls were combined. However, in the three Asian subgroups, there were no sex differences on any naming task. It is suggested that biological as well as experiential factors contribute to behavioral sex differences; and that biological (genetic) variables associated with mating group membership modify the expression of cognitive sex differences.