Having been schooled in an American elementary school for 7 years, Indian middle and high school for 7 years and returned to college in the US for what has been 2 years now, I feel like I have acquired some knowledge to answer this question.
Many of the important points have already been brought up here, but here's what I have to add:
I am of the opinion that kids in US high schools live a sheltered existence. They're in their own little shell of how the world is like. When I went to school there, I'm ashamed to say that I was too. They simply don't care about the rest of the world. It's quite amazing, really. Everything from their sports and their system of units to their culture or geography, they are unimaginably oblivious to the rest of the world. As a 5th grader ready to move to India, I myself realized that I had never even imagined a lifestyle besides the one I had been in all this while. I thought India was an abode of lots of brown people, cows, and snake charmers. This is what growing up in the US does to you.