If a group of Christians, Muslims, Jews or atheists wanted to come into classrooms and conduct lessons dealing with the advantages of their particular religions or world views, paying particular attention to their special needs and providing examples of famous members of their groups to act as role models, there would be outrage and much discussion of the separation of church and state. The reaction should be similar if the NAACP, the KKK or some other race-based organisation wanted to come in and talk about how good it was to be a particular colour.
I put talking to young children about sexuality in the same category. I don't really care what sort of educational materials these organisations make if they distribute them only to high-school students. I just do not believe that discussion of sexuality and sexual lifestyles is appropriate material for children in infant or elementary schools. Change "K-12" to "7-12" and I will be happy.