OAKLAND -- Some girls like the color blue. Some boys like to wear things that sparkle. Not all girls play with dolls, and not all boys like to play with trucks.

Kindergartners at Redwood Heights Elementary School reached those conclusions on Monday during a lesson about gender and acceptance. "Colors are colors," "toys are toys," and "activities are activities" were the mantras of a lesson designed for kindergartners and first-graders. Older children learned more about what gender means, how it's been expressed in different cultures throughout human history, and that it's possible to be both genders -- or neither.

Redwood Heights is the first elementary school in Oakland to teach children about gender identity and expression with a curriculum developed by Gender Spectrum, a San Leandro-based organization. The school's parent groups endorsed the lessons as part of an ongoing effort to make the school more welcoming, Principal Sara Stone said.

"Really, it's about reducing and dispelling stereotypes and prejudices so kids can show up to school and feel like they can learn and thrive without being stigmatized or teased," said Brett Bradshaw, a Redwood Heights parent who is also chairman of the school's LGBTQ Affinity group.

Stone said few parents expressed concern about the program, which was funded by a grant from the California Teachers Association. Late last week, however, the Pacific Justice Institute posted a news alert condemning the lessons, which were depicted in one blog as an effort to create "gender confusion" among schoolchildren. On Monday, media members from USA Today and Fox News visited the school, said Troy Flint, a spokesman for the Oakland school district.

"Kids are too young for this sort of thing," said Kevin Snider, chief counsel for Pacific Justice Institute, a conservative, Sacramento-based legal organization, who said a Redwood Heights family informed his group about the program. "These sorts of issues should be dealt with at home."

J. Crew faced a similar backlash this spring over a photograph of a child that defied traditional gender norms. A picture in its clothing catalog showed the company's creative director painting her 5-year-old son's toenails pink.

Stone said she was surprised that her school's lessons about gender differences had elicited such outrage, especially since there had been so little controversy among the school's families. The lessons do not include issues of sexual orientation, she said.

"What is wrong about teaching kids to be caring and kind?" she asked.

Oakland school district policy requires each school to create a plan to address issues of gender identity, Flint said. Children in Alameda's public schools also learn about gender differences; last year, its school board adopted an anti-bullying book list for its elementary schools that included issues of sexual orientation.

Flint said state law doesn't permit children to "opt out" of lessons other than sex education while they are at school. At least one Redwood Heights student stayed home Monday, he said, and three other families inquired about it.

On Monday morning, children in Cynthia Bagby's kindergarten class discussed whether there were, in fact, "girl colors" and "boy colors." Some giggled when Joel Baum, the trainer from Gender Spectrum, read "My Princess Boy," a nonfiction children's book by Cheryl Kilodavis about her son who liked to wear dresses and a tiara.

"That's a funny boy!" one boy said.

After the story was over, Baum and Stone asked the children how the boy must have felt when people in the book laughed at him for being different.

"It may be unusual, but we don't want to laugh at people, and we don't want to make them feel bad," Baum said.

"Clothes are clothes," he added.

"And people are people," a girl chimed in.

Read Katy Murphy's Oakland schools blog at IBAbuzz.com/education. Follow her at Twitter.com/KatyMurphy.