From the U.S. Justice Department’s “Dear Colleague” letter on transgender restroom use:

Schools across the country strive to create and sustain inclusive, supportive, safe, and nondiscriminatory communities for all students. In recent years, we have received an increasing number of questions from parents, teachers, principals, and school superintendents about civil rights protections for transgender students. Title IX of the Education Amendments of 1972 (Title IX) and its implementing regulations prohibit sex discrimination in educational programs and activities operated by recipients of Federal financial assistance. This prohibition encompasses discrimination based on a student’s gender identity, including discrimination based on a student’s transgender status.

As a condition of receiving Federal funds, a school agrees that it will not exclude, separate, deny benefits to, or otherwise treat differently on the basis of sex any person in its educational programs or activities unless expressly authorized to do so under Title IX or its implementing regulations. The Departments treat a student’s gender identity as the student’s sex for purposes of Title IX and its implementing regulations. This means that a school must not treat a transgender student differently from the way it treats other students of the same gender identity. The Departments’ interpretation is consistent with courts’ and other agencies’ interpretations of Federal laws prohibiting sex discrimination.

The Departments interpret Title IX to require that when a student or the student’s parent or guardian, as appropriate, notifies the school administration that the student will assert a gender identity that differs from previous representations or records, the school will begin treating the student consistent with the student’s gender identity. Under Title IX, there is no medical diagnosis or treatment requirement that students must meet as a prerequisite to being treated consistent with their gender identity. Because transgender students often are unable to obtain identification documents that reflect their gender identity (e.g., due to restrictions imposed by state or local law in their place of birth or residence), requiring students to produce such identification documents in order to treat them consistent with their gender identity may violate Title IX when doing so has the practical effect of limiting or denying students equal access to an educational program or activity.

A school’s Title IX obligation to ensure nondiscrimination on the basis of sex requires schools to provide transgender students equal access to educational programs and activities even in circumstances in which other students, parents, or community members raise objections or concerns. As is consistently recognized in civil rights cases, the desire to accommodate others’ discomfort cannot justify a policy that singles out and disadvantages a particular class of students.