[tsimionescu]

Let's parse that sentence carefully:

A school district may not encourage classroom discussion about [sexual orientation or gender identity in primary grade levels] OR [in a manner that is not age-appropriate or developmentally appropriate for students] .

So no discussion about gender identity or sexual orientation (so don't discuss about families with two mommies) at all in primary grade levels. Then, for all (other) grade levels, no such discussion that is not age-appropriate.