This study provides a global perspective on gender differences in performance of 9- and 13-year-olds on mathematics and science exams by reanalyzing and interpreting results on the 1991 International Assessment of Educational Progress. The analyses were performed across 20 countries that tested 13-year-olds and 14 countries that tested 9-year-olds. A random sample of 3,300 students was selected from each population at each age level; half were assessed in mathematics and half in science. The gender effect sizes on the mathematics assessment at both the subdomains level and the total scores were found to be small, especially among 9-year-olds. In general, the gender effects for science were substantially larger than those for mathematics (SD = 0.16 and 0.26 SDs on the total score, in favor of boys, for 9- and 13-year-olds, respectively). Analyses were carried out in seven selected countries-Hungary, Ireland, Israel, Korea, Scotland, Spain, and the United States. Gender differences in variability, reliability, and the structure of the intercorrelations among the subdomains were discussed as well.