A North Carolina school violated the constitutional rights of its female pupils by requiring them to wear skirts, a US federal court has ruled.
The Charter Day School, in the city of Leland, had said its uniform promoted girls as "fragile vessels" deserving of courteous and gentle treatment.
But a group of parents who challenged the policy said it put their daughters at a disadvantage compared to males.
The 4th US Circuit Court of Appeals agreed on Wednesday by a 10-6 vote.
Writing the majority opinion, Senior Circuit Judge Barbara Milano Keenan said Charter Day had "imposed the skirts requirement with the express purpose of telegraphing to children that girls are 'fragile,' require protection by boys, and warrant different treatment than male students, stereotypes with potentially devastating consequences for young girls".
According to court documents, Baker Mitchell - the school's founder - had argued the skirts were intended to preserve "chivalry", describing the word as "a code of conduct where women are regarded as a fragile vessel that men are supposed to take care of and honour".
He added the policy would ensure female students were treated "courteously and more gently than boys".
The court ruled that the dress code violated the equal protection clause of the Constitution's 14th Amendment, which prevents arbitrarily discriminatory laws from being enacted.
The defendants had argued the school was not subject to the clause because its status as a so-called charter school - or a privately-run public school - deemed it not to be a "state actor".
But the court determined that the Charter Day School not only receives public funds from the state and is subject to the state's educational requirements, but is also referred to as a "public school" in state statutes.
It has ordered hearings at the lower court level on allegations that the skirt requirement violates Title IX, a federal statute that bans gender discrimination in state and state-funded schools.
Plaintiffs in the North Carolina case were parents whose female students attend kindergarten through eighth grade at Charter Day, and were represented by the American Civil Liberties Union non-profit.
They argued the dress code had led their daughters to receive unequal treatment and limited their ability to participate in activities like recess or emergency drills.
"I'm glad the girls at Charter Day School will now be able to learn, move, and play on equal terms as the boys in school," lead plaintiff Bonnie Peltier said in a statement following the ruling.
"In 2022, girls shouldn't have to decide between wearing something that makes them uncomfortable or missing classroom instruction time."