Plaintiffs argued that Title IX and the 14th Amendment protected their rights. Government lawyers argued that the bans protect a wider swath of women.

At least half of the states in the nation have bans on transgender students competing in sports according to their gender identity, a USA TODAY review of state laws and policy documents found.

"Idaho's law classifies on the basis of sex, because sex is what matters in sports," said Alan Hurst, the Idaho solicitor general who argued for the state.