The role of achievement in mathematics during high school is a critical barrier for women. Very few who were not planning a math-related career in the 12th grade later switch into a math-related career. Math skills are highly correlated with math-related career plans, and math skills developed during high school are both an essential component of subsequent educational attainment and a significant predictor of success in establishing math-related careers independent of level of educational attainment. Only minimal sex differences in math achievement are apparent in ninth grade, but dramatic sex differences are measured in math achievement gains during the high school years. These differences are attributable to a greater participation by males in elective math courses and a greater male interest in math-related careers. (Author/PJC)