California public schools must allow transgender students to choose which restrooms to use and whether to join the girls' or boys' sports teams under a law signed by Democratic Governor Jerry Brown on Monday.
Supporters say it is the first state law to require equal access to sex-segregated school facilities based on the gender with which the student identifies instead of their biological gender.
But opponents say the law is too vague, and could lead to abuses.
Some school districts, including Los Angeles and San Francisco, already allow students to participate in sports programs and choose school facilities in accordance with their gender identity, said Carlos Alcala, spokesman for the law's author, Democratic Assemblyman Tom Ammiano of San Francisco.
Under this law, all of the state's districts would have to do that.
"There were other school districts that made it very difficult on students, so that's why we felt the law was necessary," Alcala said.
Last month, the Arcadia School District in Southern California settled a transgender discrimination lawsuit filed when a middle school student, who was born female but identified as male, was barred from using male restrooms and locker rooms at school.
Alcala said that at least one other U.S. state had policies addressing transgender student access issues, but California was the first state to enact a law mandating access to restrooms and sports teams.
Supporters said the law would provide a morale boost for transgender students, who often feel isolated and frequently endure abuse.
"It's going to send them a message that they are a part of the school community and that they are valued and that we want to see them participate fully and want to see them succeed," said Ilona Turner, legal director for the Transgender Law Center, a nonprofit legal transgender right organization that co-sponsored the bill. "That's a powerful message that, frankly, they have not been getting up to this point," Turner said.
Dozens of civil rights, gay rights and educational groups, including the American Civil Liberties Union of California and the California Teachers Association, supported the bill.
A handful of conservative and religious groups, including the California Catholic Conference and Concerned Women for America opposed it, according to documents filed by the Senate Rules Committee.
Pro-family policy organization Capitol Resource Institute opposed the bill.
"They didn't need to force this on every single California school district," said Karen England, a spokeswoman for the Capitol Resource Institute.
England said the law is too vague and provides no guidelines for implementation or to guard against abuse.
"Most Californians don't want their daughters showering or going to the restroom with boys," she said.
(Reporting by Laila Kearney in San Francisco; Editing by Sharon Bernstein and Lisa Shumaker)