Public schools must incorporate the historical contributions of gays and lesbians into lesson plans, under a law signed Thursday by Gov. Jerry Brown.

Senate Bill 48, the Fair, Accurate, Inclusive and Respectful Education Act by state Sen. Mark Leno, D-San Francisco, adds lesbian, gay, bisexual and transgender people, as well as the disabled, into the existing list of underrepresented cultural and ethnic groups listed in the state’s inclusionary education requirements.

“History should be honest,” Brown said. “This bill revises existing laws that prohibit discrimination in education and ensures that the important contributions of Americans from all backgrounds and walks of life are included in our history books.”

Leno said research shows students who learn about LGBT people find their school environments more accepting of LGBT youth, and are more likely to report that their LGBT peers are treated fairly at school.

Equality California Executive Director Roland Palencia called the new law “a monumental victory.” “Thanks to the FAIR Education Act, California students, particularly LGBT youth, will find new hope and inspiration and experience a more welcoming learning environment.”

Some conservatives opposed the bill and urged Brown not to sign it.

“Jerry Brown has trampled the parental rights of the broad majority of California mothers and fathers, who don’t want their children to be sexually brainwashed,” SaveCalifornia.com President Randy Thomasson said. “The only way parents can opt-out their kids from this immoral indoctrination is to opt them out of the entire public school system, which is no longer for morally sensitive parents and their children.”

This is “the eighth school sexual indoctrination law forcing immorality on kids in California K-12 schools,” he added, and “the broad majority of parents don’t want their children to be made to admire homosexuals, bisexuals and transsexuals.”

The state Senate approved the bill in April on a 23-14 vote; the Assembly passed it last week on a 50-26 vote.

The new law will enrich classroom lessons by better reflecting the state’s diversity, State Superintendent of Public Instruction Tom Torlakson said in a statement. “Our history is more complete when we recognize the contributions of people from all backgrounds and walks of life.”

Due to budget cuts, the state won’t create K-8 curriculum materials until 2015. But when the law goes into effect in January, school boards will be prohibited from sponsoring activities that promote discrimination or from adopting textbooks or instructional materials that reflect adversely on the gay and lesbian population, he said.

Mike Langley, a high school history and economics teacher and president of the Mt. Diablo district teachers union, said he wasn’t sure how the district would choose to integrate the new law into lesson plans. He said he has taught about African-American and Latino contributions in the context of larger lessons, rather than creating lessons focused specifically on certain segments of the population. “As a teacher, I would not feel there’s a problem with incorporating everything involving history in our lessons.”

The West Contra Costa district has an LGBT Youth Commission and provides staff development and sensitivity training to ensure that all students feel safe, said Marin Trujillo, district spokesman. The district would look to the state Department of Education for guidance regarding best practices and suggested curriculum modifications, he said, which could take a couple of months to develop.

Staff writer Neil Gonzales contributed to this report.

Contact Josh Richman at jrichman@bayareanewsgroup.com and Theresa Harrington at tharrington@bayareanewsgroup.com.