Redwood Heights Elementary School, in Oakland, is in the hot-seat after the school decided to educate students about gender diversity.

On Monday and Tuesday, students of every grade were taught what the school called age-appropriate lessons about gender differences. Some lessons included all-girl geckos, a transgender clownfish, and boy snakes who act "girly" reports the San Francisco Chronicle.

"That's a lot of variation in nature," Gender Spectrum trainer, Joel Baum, told the students. "Evolution comes up with some pretty funny ways for animals to reproduce."

Principal Sara Stone said the lesson on gender differences was part of a larger effort to control bullying in the school, something parents supported last year.

However, after the lessons began, several parents felt discussion in the classroom was too much.

The Pacific Justice Institute, a conservative organization, said teaching children that there may be more than two genders, "does not represent the values of the majority of families in Oakland,"

The $1,500 cost of training was funded by a grant from the California Teachers Association.