In this article, Howard Wainer and Linda Steinberg examine sex differences in scores on the mathematics section of the Scholastic Aptitude Test (SAT-M) by comparing the SAT-M scores of men and women who performed similarly in first-year college math courses. Matching almost 47,000 men and women on type of math course taken and grade received, the authors found that, on average, women had scored about 33 SAT points lower than men who had taken the same course and received the same grade. The authors then analyzed the same data using prospective regression analysis and found somewhat larger sex differences in the same direction. Though the data do not allow any conclusions about the cause of these differences in SAT-M scores,they do provide evidence of sex differences in the validity of the SAT-M as a predictor of college math performance. The authors conclude with a discussion of how educators might respond to possible inequities in test performance.