It doesn't help when every adult says to them from a very young age "aren't you clever/smart etc". Drives me crazy because it has never been said that way at home.
Exactly.
Our school district has self-contained gifted elementary and middle school programs housed in larger schools, so that there are the magnet kids, and then there are the "zonies". Whether or not the magnet kids are encouraged to feel superior at home, the schools actively promote the We Are The Master Race attitude. For example, at gifted open house last fall, one of the speakers (eighth grade) assured the incoming sixth graders not to worry, that it's not required to interact with the zoned kids most of the time. Likewise, at a SAC meeting the principal commented that math team wasn't available for the school as a whole because it's not likely that there'd be a zoned kid who would qualify, after all. By the time the kids have been in this atmosphere a few years (and through no real fault of their own), some of them are absolutely insufferable.
