A transgender girl in Mississippi did not participate in her high school graduation ceremony because school officials told her to dress like a boy and a federal judge did not block the officials’ decision, an attorney for the girl’s family said Saturday.

Linda Morris, staff attorney at the American Civil Liberties Union’s Women’s Rights Project, said the ruling handed down late Friday by U.S. District Judge Taylor McNeel in Gulfport, Mississippi, “is as disappointing as it is absurd.”

“Our client is being shamed and humiliated for explicitly discriminatory reasons, and her family is being denied a once-in-a-lifetime milestone in their daughter’s life,” Morris said. “No one should be forced to miss their graduation because of their gender.”

The ACLU confirmed that the 17-year-old girl — listed in court papers only by her initials L.B. — would skip the Saturday ceremony for Harrison Central High School in Gulfport, about 160 miles (260 kilometers) south of Jackson.

The student “has met the qualifications to receive a diploma,” according to Wynn Clark, attorney for the Harrison County School District.

The ACLU sued the district Thursday on behalf of the student and her parents after Harrison Central principal Kelly Fuller and school district superintendent Mitchell King told L.B. that she must follow the boys’ clothing rules. Graduating boys are expected to wear white shirts and black slacks, while girls are expected to wear white dresses.

L.B. had selected a dress to wear with her cap and gown. The lawsuit said L.B. had worn dresses to classes and extracurricular events throughout high school, including to a prom last year, and she should not face discriminatory treatment during graduation.

King told L.B.’s mother that the teenager could not participate in the graduation ceremony unless L.B. wears “‘pants, socks, and shoes, like a boy,’” according to the lawsuit.

Clark wrote in court papers Friday that taking part in a graduation ceremony is voluntary and not a constitutionally protected right for any student.