After a lesbian student at Jesse Bethel High School in Vallejo joined with the American Civil Liberties Union  in 2008 to accuse the local school district of discrimination, district officials agreed as part of a settlement to show films and assign homework depicting same-sex families, beginning in elementary school.
But one night last November, more than a dozen parents, rallied by community religious leaders, attacked the school board, asserting that their rights were being violated because they had no control over whether their children received such lessons.
“No one should take my right to tell me what can be shown to my child,” Cookie Gordon, a mother of two, told the board.
The clash was one of several related controversies at Bay Area schools. Polls show that the public’s stance against same-sex marriage  is softening, and education about gay issues has expanded dramatically in recent years around the country, but experts suggest that the battle over what should and should not be a part of public school curriculums has just begun.
Ritch Savin-Williams, a professor of human development at Cornell University , said that the question of gay men and lesbians in the military was now over the hump, and that same-sex marriage was getting close to getting over the 50 percent mark in terms of popular support in California. But the issue of school curriculums, he said, “hits at something that’s far more difficult, and that’s children.”
California is poised to take a step sure to sharpen the debate. A bill introduced in December by State Senator Mark Leno, Democrat of San Francisco, would require all of the state’s history textbooks to include figures and events in gay history and portray them “in a positive light.”
To the many educators and gay rights advocates like Mr. Leno — one of the first two openly gay men elected to the Legislature — the need for the law is as self-evident as it is urgent.
“People oppose and fear the unfamiliar,” Mr. Leno said in an interview. “When grade-school students understand the arc of the L.G.B.T. movement over 40 years, that otherness begins to dissipate. That’s desperately needed right now.”
Educators point to several recently publicized suicides by gay teenagers as evidence that anti-gay bullying needs to be addressed head-on, in part by integrating gay studies into the curriculum.
Political observers believe that with Gov. Jerry Brown  in office, Mr. Leno’s legislation is likely to become law. A similar measure passed the Legislature in 2006 but was vetoed by Gov. Arnold Schwarzenegger . The Senate Education Committee is expected to take up the bill, the first of its kind in the country, this spring.
Conservative groups have promised to fight the Leno bill.
“These controversial issues don’t belong in the classroom, no matter how many times people vote on marriage,” said Karen England, a member of the State Central Committee of the California Republican Party . “The homosexual activists have repeatedly been pushing for more and more in sexual curriculum when our kids can’t read or write.”
For parents like those who attended the Vallejo board meeting in November, it is a question of their right to control their children’s education. State law does not allow parents to remove their children from particular lessons that are part of a set curriculum.
At the meeting, a mother angrily waved a crossword puzzle assigned her 9-year old daughter that included the word “lesbian.” (The clue: “Two women who love each other in a romantic way.”)
The parents were backed by Pastor P. Daniels Jefferson, the popular leader of the Vallejo Faith Organization, an influential evangelical Christian umbrella group. Mr. Jefferson said that while he opposed bullying, Vallejo’s Christians felt that their voice was being suppressed.
“When you call us haters, or bigoted, or unintelligent because we believe in God’s word,” Mr. Jefferson said, “that’s hate, that’s bigotry.”
Mr. Jefferson said Mr. Leno’s bill was another step in what he labeled a long-running gay political agenda to “queer” the schools. He called the next 20 years the “most critical” period in the state’s debate over gay rights. “Today’s children are tomorrow’s voters,” Mr. Jefferson said, “and, believe me, nobody’s stupid. People know that.”
In 2008, some of the most powerful television advertisements broadcast by the campaign for Proposition 8 , the California ban on same-sex marriage, evoked images of children’s being taught same-sex marriage in school without parental knowledge.
Despite its reputation as a bastion of gay-friendliness — or perhaps because of it — the Bay Area has emerged as a focal point in the gay education debate. In Alameda, a group of parents sued the school district in 2009 after discovering that their children were reading “And Tango Makes Three” — a book about two male penguins raising a young penguin — as a part of a pro-tolerance lesson. District officials said they introduced the lesson after grade-school children were heard using gay slurs in the hallways.
The San Francisco Unified School District has what some consider the most gay-friendly curriculum in the country, publishing general guidelines to help teachers teach words like “gay” and “heterosexual,” beginning in kindergarten. But beyond the general guidelines, there can often be distinctly different approaches from school to school.
Jenn Bowman, a world history teacher at Mission High School, said colleagues at her former school, Roosevelt Middle School, questioned whether it was appropriate for her to let her students know she is gay.
The atmosphere is altogether different at Mission High, Ms. Bowman said, where Gay Pride Month is celebrated exuberantly with schoolwide assemblies. There is a large drag show each year, in which the principal is usually the star. Ms. Bowman thinks it is appropriate to teach gay history. “Right here, in the classroom, is totally where it needs to start,” she said.
Across the country, educators say that pro-tolerance curriculums, as well as open discussions of homosexuality in the classroom, have grown much more prevalent in the last 15 years.
When Groundspark, a San Francisco firm that produced the videos that Vallejo parents objected to, created its first film, “It’s Elementary — Talking About Gay Issues in School,” in the mid-1990s, the producers struggled to find a handful of schools where teachers were teaching about lesbian and gay families. The film caused an uproar when it was shown on public television in 1999, said Debra Chasnoff, the producer.
Today, the company receives orders from more than 4,000 schools and school districts, from Huntsville, Ala., to Oshkosh, Wis.; from Stockholm to Tokyo.
In 1998, when Carolyn Laub founded the Gay-Straight Alliance Network, a co-sponsor of Mr. Leno’s bill, the organization consisted of member clubs at 40 schools. Now there are 4,000 clubs nationwide, Ms. Laub said.
Some students said that if it were not for the school lessons, their parents would most likely not raise issues regarding their gay peers.
“I don’t think we’d talk about it,” said Lorenz Mateo, a 16-year-old junior at Bethel High in Vallejo. “It’d be mad awkward.”
Other students said that while they doubted that the Groundspark films would change behavior in the hallways, where “gay” is often an interchangeable synonym for “dumb,” watching them left an impression nonetheless.
“I know I say those things,” said Julian Rodriguez, a 16-year-old Bethel junior. “But it makes you think. It puts that thing in the back of your head.”