This article reviews research set to be published next year (why the wait?), which indicates that for many intelligent kids, particularly boys, the pressure is on to underachieve, lest they be bullied. Further (and obvious as well), the poorer the school performs, the more pressure there is to dumb yourself down. From the article:
The study, to be published in the Sociological Review next year, shows how difficult it is for children, particularly boys, to be clever and popular. Boys risk being assaulted in some schools for being high-achievers. To conform and escape alienation, clever boys told researchers they may "try to fall behind" or "dumb down".
This particular study was conducted in England, but I have little doubt that these issues are at least as problematic in American schools. I remember this kind of garbage when I was a kid, though I also remember it was worse at certain schools I attended than at others. I can recall cringing on days when honor roll was posted, just waiting for the forthcoming abuse; I can only imagine what it's like today, 20+ years later.
I don't work with kids, so I'm not sure what the current thinking is at schools with respect to strategies to deal with this. I do suspect that for many parents who rank school as a prime issue in terms of where to live, paying for private school, etc., it is the culture of achievement (or lack thereof) that is at least as important as the quality of teachers, class opportunities, etc. that factors into their decision. Pressure to underachieve is just depressing, and if you've got a bright kid, it must be so frustrating to consider underachievement might be socially reinforced. Again, not sure what the current thinking is on this, but I'm assuming there are efforts to address this sort of thing.