Over two dissenting votes, the justices left in place lower court rulings that found the policy unconstitutional.
The case involved former high school student “Gavin” Grimm, a biological female, who filed a federal lawsuit after she was told she could not use the boys bathroom at her public high school.
Justices Samuel Alito and Clarence Thomas voted to hear the board’s appeal.
The Gloucester County, Virginia, school board’s policy required Grimm to use restrooms that corresponded with her biological sex — female — or private bathrooms.
Seven years ago, Grimm was barred from using the boys restroom when she was a 15-year-old student at Gloucester High School.
She sued a year later, and her case has worked its way through the courts ever since.
After learning that the Supreme Court refused to hear the case, Grimm, now 22, said that her long court battle is over.
“We won,” she tweeted. “Honored to have been part of this victory,” she added.
David Corrigan, an attorney for the school board, did not immediately respond to email and voice mail messages seeking comment.
In its petition asking the Supreme Court to hear the case, the school board argued that its bathroom policy poses a “pressing federal question of national importance.”
The board argued previously that federal laws protect against discrimination based on sex, not gender identity.
Because Grimm had not undergone sex-reassignment surgery and still had female genitalia, the board’s position has been that she remained anatomically a female.
The American Civil Liberties Union, which represented Grimm in her yearslong lawsuit against Gloucester, argued that federal law makes it clear transgender students are protected from discrimination.
Adapted from reporting by Associated Press.