idk my parents never hid anything from me. Those movie ratings meant nothing in my family, my parents wanted me to see real life, and I did. I turned out a lot better then those kids whose parents sheltered them from sex and drugs.
I think its good to show kids that sorta thing at a young age, it kind of hinders any curiosity. For me it did at least. Well it was a combination of that and my parents threatning me with my life if i ever impregnanted a girl before i was married or used drugs.

(pops is a marine ahaha)
But i dont think theres anything wrong, if a schools showing it for educational purposes, im sure its been approved for that purpose. That plus im a camp counselor with 12 year olds, trust me they know alot more and see more then you may think...