Foes of a law that mandates schools teach about the historical contributions of gay, lesbian, bisexual and transgender people have conceded they don't have sufficient voter signatures for a repeal effort.

Starting as early as the 2013-14 school year, Senate Bill 48 (SB48) or the FAIR Education Act, sponsored by state Senator Mark Leno, a Democrat from San Francisco, requires the California Board of Education and local school districts to include the curriculum in their lesson plans.

Opponents of the law had until Wednesday to collect the signatures of 504,760 registered voters to qualify for the next statewide ballot.

In an email to supporters, the group spearheading the effort, Stop SB48, conceded they had come up short.

“Unfortunately we did not collect enough signatures to qualify the referendum to overturn SB48,” the group said. “That law will be in place in our schools at the first of next year.”

“In the end, 90 days was too short a time to accomplish such a large task.”

Supporters of the law note that national conservative organizations largely kept out of the fight, leading to the speculation that they are planning a November 2012 ballot initiative.

“We always imagined they would try to take another bite at the apple in November,” said Rebekah Orr, a spokesperson for Equality California, the state's largest gay rights group. “[W]e need to be prepared for them to qualify in November.”

(Related: Group accuses foes of California gay history law SB48 of tricking voters.)