In the SanFran Chronicle:

All [California] state schools are required to have a specific plan to address safety and other issues related to sexual orientation and gender identity.

Gender harassment can start at very young ages, often before kindergarten, and it is not uncommon for children who step outside of narrow gender expectations, whether in their clothing, hair, toys or styles of play, to become the targets of mistreatment by other children," said district spokesman Troy Flint in an e-mail.

So on Monday, Redwood Heights fourth-graders listened intently to descriptions of biological gender, gender expression and identity.

Gender isn't something that's cut and dry, Baum said.

"Earrings used to be something only girls and pirates wore," Baum said to fourth-grade giggles.

And what's on the outside doesn't necessarily reflect what's on the inside, he said.

"People can feel like girls," he said. "They can feel like boys. They can feel like both, and they can feel like neither."