The Civil Rights Act of 1964 protects minorities and various other marginalized groups of Americans from discrimination in employment, housing, and education. The law is constantly evolving, however. In 1972, Title IX was added to the Civil Rights Act in an effort to ensure greater gender equality in education, including collegiate sports.
Title IX states the following:
No person in the United States shall, on the basis of sex, be excluded from participation in, be denied the benefits of, or be subjected to discrimination under any education program or activity receiving federal financial assistance...
Title IX prohibits sex discrimination at all educational levels, from elementary to higher education, as long as the institution receives federal funding. But there are some notable exceptions to the law, which are listed below. See Title IX and Sex Discrimination in Amateur Athletics and Liability Under Title IX: Parties and Standards to learn more.
Schools are permitted to discriminate for reasons of selecting certain vocal ranges or voice characteristics. This means all-female or all-male choruses may be perfectly legal, without violating the terms of Title IX.
Elementary, middle, and high schools are permitted to conduct separate human sexuality sessions for boys and girls, owing to the unique biological differences in the sexes. This is only applicable to classes (or activities) that deal exclusively with human sexuality.
For physical education (or other school-sponsored activities), students may be separated by gender in sports that involve bodily contact, such as wrestling or football. Also, it is not a violation of Title IX if students are separated by objective performance standards and it results in all-female or all-male groups (for example, males generally have more upper-body strength than females).
However, if this objective performance standard ends up having an adverse effect on any one gender group -- such as excluding predominantly males or females from participation -- then schools must find another standard. The ability to benchpress X number of pounds, for example, should not be the criteria for joining the track and field team.
Whenever any of the aforementioned exemptions results in separate educational or athletic programs, the school must maintain comparable facilities and services for both groups.
Contact an education attorney if you have more questions about sex discrimination in education and protections under Title IX.