What the Federal Decision to Stand With Trans Girl Means for School Locker Rooms Nationwide

— -- The U.S. Department of Education has announced that a suburban Chicago school district is violating the rights of a transgender student by refusing her access to the girls' locker room despite the fact that she identifies as a girl, according to a 14-page letter to the district.

The letter's findings conclude a nearly two-year investigation made by the DOE's Office for Civil Rights (OCR) after the trans student, with the help of the American Civil Liberties Union (ACLU) in Illinois, filed a federal complaint against Township School District 211 in Palatine, Illinois, in December 2013.

The school district had been denying the trans girl's request to have unrestricted access to the girls' locker room, forcing her to change and shower in a separate facility that made her feel "stigmatized" and "not like a 'normal person,'" she said, according to a statement made by the ACLU of Illinois.

Though the district recognized the student as female in its computer systems and allowed her to have unlimited access to the girls' restrooms, it said granting her the "option to change her clothes in the girls’ locker room would expose female students as young as fifteen years of age to a biologically male body," according to the DOE's letter.

The OCR found that such reasoning was discrimination "on the basis of sex," which violated Title IX, a comprehensive federal law that prohibits discrimination on the basis of sex in any federally funded education program or activity. Title IX is the same law that mandates parity between male and female athletic programs.

The DOE's letter to the school added that to date, "efforts to resolve this complaint voluntarily with the District have not been successful."

The DOE also threatened to take "enforcement action" against the school district if compliance or an agreement wasn't reached within 30 days of the letter dated Nov. 2, 2015, putting the district at risk of losing millions in federal funding.

District Superintendent Daniel Cates said that the district is standing by its original decision. In a guest column for local newspaper The Daily Herald, he acknowledged that the "potential loss of federal funds is significant, but we believe the loss of appropriateness, reason and privacy for teenagers is also significant."

Cates told ABC News today that the district is "disappointed" in the DOE's findings and that "we do not agree we’re violating any law, and we believe the accommodations we’ve offered support our trans students and balance the privacy rights of all of our students."

Advocates said the issue is one of equal rights.

The DOE's findings in its recent letter is putting "schools nationwide on notice that they must protect the rights of trans students and ensure that those students can access school programs and facilities without discrimination," according to Michael Silverman, executive director of the Transgender Legal Defense and Education Fund (TLDEF) and professor of law at Fordham University.

"Additionally, the DOE's threat of enforcement action is telling schools nationwide that failure to protect trans students from discrimination can and will result in legal action," Silverman told ABC News.

The trans student in the center of the case has not been publicly identified and is declining to speak with the media, according a statement from the ACLU of Illinois.