SAN FRANCISCO (AP) — California is preparing for the first state law in the U.S. spelling out the rights of transgender students, but it's possible the law could be suspended within days of its Jan. 1 launch if an effort to repeal it makes it onto voters' ballots later in the year.

The law is the nation's first requiring public schools to let transgender children use sex-segregated facilities and participate in the gender-specific activities of their choice.

California's law comes amid legal challenges across the U.S. involving transgender students filing actions for the right to use facilities that match their expressed identities.

To obtain a public vote on the law, passed by the legislature and signed by Gov. Jerry Brown, a coalition of conservative groups called Privacy for All Students has collected hundreds of thousands of signatures. Counties have until Jan. 8 to verify them.

"We don't know what's going to happen when kids come back from their holiday vacation," said Republican state Sen. Steve Knight, who voted against the law. "Are there going to be 15-year-old girls talking in the bathroom and in walks a boy? What are they going to do? Scream? Run out?"

The California School Boards Association is acting on the assumption that the law will stand and that, even if it does not, existing state and federal anti-discrimination laws already compel schools to accommodate transgender students.

The association has advised schools to handle requests on a case-by-case basis but to be prepared to make private changing arrangements both for transgender students and for classmates who might object to dressing with them.

"We did strike a balance between the sensitivities associated with gender identity, not only for those students who experience a change in their gender status but the students who would be in the same facilities, in the same classrooms and on the same teams," General Counsel Keith Bray said.

The possibility that the law could be overturned worries Ashton Lee, 16. Born a girl, Ashton recently told his parents and school administrators that he was transgender.

Ashton lobbied for the law and thinks his public activism helped persuade his school to acknowledge his gender identity when school resumed in August. He now is allowed to use the boy's restrooms. Similar adjustments have been made for five transgender classmates.