Now in eighth grade, Pepper-Jackson has identified as female for five years — nearly half her life, the court noted. Since elementary school, she has only participated in girls’ sports. She has a birth certificate that identifies her as female. And she takes medication to block male puberty and undergo female puberty, which the court said was key to its decision.

Pepper-Jackson “has never felt the effects of increased levels of circulating testosterone,” so “the fact that those who do benefit from increased strength and speed provides no justification — much less a substantial one — for excluding [her] from the girls cross country and track teams,” the judges wrote. To force her to play on a boys’ team or not play at all “would expose [her] to the same risk of unfair competition — and, in some sports, physical danger — from which the defendants claim to be shielding cisgender girls,” the court said, as she would be “sharing the field with boys who are larger, stronger, and faster than her because of the elevated levels of circulating testosterone she lacks.”

Requiring her to do that violates federal civil rights law, the court said. That does not mean “we do not hold that government officials are forbidden from creating separate sports teams for boys and girls or that they lack power to police the line drawn between those teams,” the judges added. Nor does it mean that federal law “requires schools to allow every transgender girl to play on girls teams, regardless of whether they have gone through puberty and experienced elevated levels of circulating testosterone.” Only in Pepper-Jackson’s “particular case” is the ban discriminatory, it said.

Tuesday’s decision was written by Judge Toby J. Heytens, a Biden appointee, and joined by Judge Pamela Harris, an Obama appointee. Judge G. Steven Agee, an appointee of George W. Bush, dissented and said he “hope[d] that the Supreme Court will take the opportunity with all deliberate speed to resolve these questions of national importance.”

The Christian conservative group Alliance Defending Freedom, which backed this law and others restricting trans rights, indicated that an appeal may be coming. The ruling “undermines equal opportunities and contradicts both biological reality and common sense,” legal counsel Rachel Rouleau said.

What the Supreme Court might do is unclear, despite its conservative slant. On Monday the high court allowed Idaho to enforce a criminal ban on gender-affirming medical treatment for trans minors. But the court also declined last year to let West Virginia’s law be enforced while it was being challenged in the 4th Circuit.

The 4th Circuit — which also handles appeals from federal courts in Maryland, Virginia, North Carolina and South Carolina — was once the most conservative appellate court in the country; now it is a trailblazer in the realm of trans rights. It was the first appellate court to recognize a trans student’s right to use the bathroom that reflected his gender, a ruling the Supreme Court let stand. It was also the first to label gender dysphoria, or a disconnect between one’s gender and assigned sex, as a disability protected under federal law. The court is also considering whether state health plans must cover gender-affirming treatments.

Joshua Block of the ACLU, which represented Pepper-Jackson, said the case was part of “a string of federal courts ruling against bans on the participation of transgender athletes and in favor of their equal participation as the gender they know themselves to be.” Courts from Arizona to Connecticut have sided with transgender students. While some of those rulings have been put on hold on appeal, he said, no appellate court has ruled against trans athletes on the merits.

While a majority of Americans support laws protecting trans rights in schools and elsewhere, according to a 2023 Washington Post-KFF poll, most also believe trans women and girls should not be allowed to compete in sports with other women and girls and that gender is determined at birth. Republicans have seized on those fissures, supporting laws at the state and federal level that limit trans rights. While there was national outrage in 2016 when North Carolina banned trans people from using the bathrooms corresponding to their gender identity, recent legislation in the state targeting trans minors provoked little reaction. West Virginia passed its law in 2021, declaring that students “whose biological sex determined at birth is male” cannot compete on girls’ teams.

Trans advocates say the question of who should play women’s sports, while politically heated, is blown out of proportion. In Kentucky, a state law similar to the one in West Virginia affected only a single student athlete. Competitive sports leagues have their own rules regarding trans athletes.

When she first sued over the ban, Pepper-Jackson said she “regularly finishes near the back of the pack” in track-and-field. By the time the decision came out, she was placing higher in some events while remaining behind in others. Agee argued that those results were evidence of a biological advantage and of unfairness. “Biological girls participating in these events were displaced by and denied athletic opportunities because of” Pepper-Jackson, he wrote.

The majority agreed with Pepper-Jackson that merely placing ahead of another girl in competition did not mean she had a biological advantage. There are few studies on transgender performance, but research indicates that only after going through male puberty do boys have a physical advantage over girls in sports.

The Biden administration has proposed rules that would allow federally funded schools to block trans students from playing sports only if the decision was justified based on the sport involved, the age of the students and the level of competitiveness. Those rules, when released, could change how courts analyze similar cases in the future, Block said.

Pepper-Jackson also challenged the state law under the 14th Amendment’s equal protection clause. But the judges said the factual record was not well-developed enough to say West Virginia had no “important state interest” in keeping Pepper-Jackson off the team — a defense that doesn’t exist under federal civil rights law.