It's pretty uncommon among industrialized countries to keep education (more or less) unified as late as 12th grade, and under these circumstances I can see intellectuality coming to be associated with a subcultural alignment; whereas under something like the German system, classes would end up being fragmented along giftedness lines before strong subcultural cliques form.

That's an interesting factor, but I question whether it is a cause, or a symptom (which potentially has effects similar to the original cause). I ask "Why did America choose to deny gifted and talented children a chance to develop their abilities to the fullest for longer than any other country?" (I'd love to see a citation for that by the way!)

I think the root cause might actually be the "immortal declaration" of Thomas Jefferson, located in the opening of the United States Declaration of Independence:

We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights...

When a country's most important concept is human rights, and the most prominent argument in support of human rights is the belief that you are created equal, you're essentially in a situation where your country was founded on the belief that giftedness does not exist.

It seems to me that when people reject gifted identity claims, their true objection is not that it's arrogant to claim high status* or that it's socially unacceptable to say good things about yourself* but that they're interpreting "created equal" to mean something similar to "equal abilities" or "mentally equal" and experience conflict(s) along the lines of:

1. If I some people are not equal, does that mean human rights don't exist?

2. If I agree that this person is unequal and they're the better one, do I have to give up my rights to them or give them special treatment?

3. If this person is claiming to be unequal, are they also trying to demand the right to take my rights away or extract something extra from me so they can have unequal rights?

4. If I let myself believe that people aren't equals, is that morally wrong?

Even though I think the problem runs deeper than the theory you presented, I am glad to have it. If America is denying children the chance to develop to the fullest for longer than other countries, that's certainly going to have some kind of an effect and it's good additional information to have. Thank you; +1 karma.

* There are plenty of other status claims and good things you can say about yourself that don't provoke negative reactions - see the thought experiments in this thread.