In 1972, sex-based discrimination in public and private schools receiving federal funds was prohibited by federal legislation in the form of Title IX. Title IX has been interpreted, reinterpreted, and misinterpreted in many cases to refer (more or less) to athletic programs and the scholarships associated with them, but the law also covers discrimination in academics.
Before 1972, high schools typically segregated classes according to sex. Boys were encouraged to take advanced math and science courses, while girls were dissuaded or even prevented from enrolling in those courses. Although Title IX had a profound impact on girls in athletics, the law also influenced the academic experiences of girls. Today, participation in high school athletics programs is nearly 50% female. Largely as a result of Title IX, there are currently no restrictions on course enrollment for female students.