PLOMIN, ROBERT, and FOCH, TERRYL T. Sex Differences and Individual Differences. CHILD DEVELOPMENT, 1981, 52, 383-385. Sex differences and their relationship to individual differences were examined for Maccoby and Jacklin's sex differences summaries and for a diverse set of measures of specific cognitive abilities and objective personality assessments for 216 school-age children. Although verbal ability is reputedly one of the most well-established cognitive sex differences, sex accounts for only about 1% of the variance of verbal measures. If all we know about a child is the child's sex, we know next to nothing about the child's verbal ability. The other measures of specific cognitive abilities and objective personality assessments yielded similar results. In general, average differences between groups appear to be trivial compared with individual differences within groups.