Historically, a person's gender was determined at birth. But in recent years, some have argued that their "gender identity" is different from their gender at birth. For example, while born a biological male, a person comes to identify with the female gender. Such persons are commonly referred to as "transgender” individuals. Some of them have surgery or hormonal therapy to change some of their physical characteristics, but many do not.
On May 13, 2016, the Civil Rights Division of the US Department of Justice (DOJ) issued a letter advising schools receiving federal financial assistance of their obligations under a federal law (Title IX of the Education Amendments of 1972) regarding transgender students. The letter warns schools that "they have a responsibility to provide a safe and nondiscriminatory environment for all students, including transgender students," and that a failure to do so may lead to loss of federal financial assistance under federal programs.
The letter addresses restrooms and locker rooms as follows: "A school may provide separate facilities on the basis of sex, but must allow transgender students access to such facilities consistent with their gender identity. A school may not require transgender students to use facilities inconsistent with their gender identity or to use individual-user facilities when other students are not required to do so. A school may, however, make individual-user options available to all students who voluntarily seek additional privacy."