The Education and Justice Departments will send a letter Friday to every public-school district in the country notifying school administrators that discrimination against transgender students violates federal civil-rights law.

In the letter, which offers the most detailed federal guidance yet for educators on transgender students and their rights, the departments interpret anti-discrimination laws to apply when a parent or guardian tells school administrators about their child’s gender identity.

Disclosing a transgender student's birth name or his or her sex assigned at birth, the letter warns, could also violate the student’s rights guaranteed under FERPA, the federal statute on privacy in educational settings.

From there, the departments outline how Title IX forbids discrimination on the basis of gender identity in a variety of school functions, including housing, athletics, and single-sex classrooms. Other activities, including graduation ceremonies and yearbooks, are also covered.

The letter also strongly sides with transgender students on the issue of restrooms and locker rooms, which have become a flashpoint nationwide in debates about transgender rights. In the guidance letter, schools are told not to discriminate against students who choose to use restrooms that correspond to their gender identity.