A North Carolina charter school's requirement that girls wear skirts based on the view that they are "fragile vessels" deserving of "gentle" treatment by boys is unconstitutional, a federal appeals court ruled on Tuesday.

The 4th U.S. Circuit Court of Appeals ruled 10-6 that Charter Day School violated three female students' equal protection rights by adopting the skirts policy based on gender stereotypes about the "proper place" for girls in society.

The school implemented a dress code that its founder, businessman Baker Mitchell, in an email and testimony said would "preserve chivalry" and ensure girls are treated "courteously and more gently than boys."

The state-funded school in Brunswick County argued the Equal Protection Clause of the U.S. Constitution's 14th Amendment did not apply to it because it was a private entity, not a "state actor."

But U.S. Circuit Judge Barbara Milano Keenan said it was one since North Carolina delegated to it its duty to provide free, universal education to students. A contrary ruling would mean North Carolina could ignore "blatant" discrimination, she said.

The Richmond, Virginia-based court also allowed the students to pursue a claim under Title IX, a federal law that prohibits sex discrimination in federally-funded education.

The ruling "is a victory for North Carolina's students attending public charter schools, and should put charter schools across the country on notice that they must follow the same rules as traditional public schools when it comes to guaranteeing students' equal educational opportunities," said Galen Sherwin, the students' lawyer at the American Civil Liberties Union.

Aaron Streett, the school's attorney, called the ruling "mistaken and harmful," saying it contradicted U.S. Supreme Court precedent and "limits the ability of parents to choose the best education for their children."

The six dissenting votes were all from Republican-appointed judges.