The U.S. Justice Department has sided with a transgender teenager who alleges that a Virginia school board’s restroom policy is discriminatory.

Gavin Grimm, a 16-year-old rising junior, filed a lawsuit against the Gloucester County, Va., school system with the help of the American Civil Liberties Union claiming that he should be allowed to use the school system’s communal restrooms and not “alternative” facilities just for transgender students. Grimm was born female and identifies as male.

In a statement of interest filed Tuesday, the Justice Department argues that the Gloucester County school board’s policy violates Grimm’s rights, and federal officials are seeking to ensure that “all students, including transgender students, have the opportunity to learn in an environment free of sex discrimination.”

ACLU lawyer Joshua Block, who oversees the group’s lesbian, gay, bisexual, transgender and HIV issues, said in a statement that transgender students “should be able to use the restroom without being stigmatized and humiliated for being who they are.”

Until December, Grimm had used the boys’ restrooms for seven weeks without any issues. Then, amid pressure from parents, the school board voted 6 to 1 to restrict girls’ and boys’ bathrooms to students of “the corresponding biological genders.”

“I just want to use the restroom in peace,” Grimm said in a statement. “Since the school board passed this policy, I feel singled out and humiliated every time I need to use the restroom.”

Justice Department officials wrote that Grimm should be allowed to use the male restrooms at Gloucester High School as a matter of mental health. It also said discriminating against transgender students could be a violation of the federal Title IX regulations that aim to prevent discrimination on the basis of gender.

“Singling out transgender students and subjecting them to differential treatment can also make them more vulnerable to bullying and harassment, a problem that transgender students already face,” according to the Justice document. The filing also cites figures showing that more than 90 percent of LGBT students in middle school and high school reported being verbally harassed and about half said they were attacked physically.

“Allowing transgender students to use the restrooms consistent with their gender identity will help prevent stigma that results in bullying and harassment and will ensure that the District fosters a safe and supportive learning environment for all students, a result that is unquestionably in the public interest.”