with the internet and boards like this, I don't think that most jr high boys will get past puberty without having seen pretty good pictures of natural skin- which would lead to real world investigation if he is so inclined...
plus our world is becoming much more diverse, and more american teens are missing the knife as they grow up- so more american uncut cock is more normal. I wouldn't expect it to be as much of a deep mystery as it might have been in the 70s.
On the opposite side of things, growing up there were team showers at all of my schools- and that seems to be a thing of the past, so (sadly) I think nudity norms are changing in our society.
It's such a contrast- becoming a more virtually open and sexualized society, and yet more closed and homophobic modest one at the same time.