It is the school district's job to decide what to teach. A non-discriminatory policy will not change that. The Bible says it is wrong to be lesbian or gay. Some people read the Bible that way, but others don't. Schools have to respect everyone's differences, and they may not impose one set of beliefs on everyone.
Research shows that sexual orientation exists in everyone at an early age, perhaps even at birth.
Adults don't really influence a student's sexual orientation. Instead, having positive role models, both gay and straight, shows students that sexual orientation is just one of many different aspects of a person's identity. It doesn't matter if someone is actually gay or straight. If a person is mistreated because someone else thinks they are gay, they've been discriminated against on the basis of sexual orientation. It doesn't matter if they really are gay or not.