I agree with mithawk's analysis.
Regarding the OP's anecdote, I would never tell another parent I was glad for competitive reasons that her child would be leaving my child's school. Besides being tactless, it ignores the fact that parents of other bright kids, and the kids themselves, are good sources of information about educational opportunities.
The anecdote does raise the question of whether the advantages of being with lots of other smart kids (probably learning more, having more like-minded peers) outweighs the disadvantages (lower class rank). For college and graduate school I think one wants to attend the most selective school possible, since (among other reasons) employers care about school selectivity. For high school, it is not clear to me that attending a Stuyvesant or a Phillips Exeter Academy boosts one chances of being admitted to an Ivy, since many students at those schools will be applying to Ivies. OTOH, the connections one makes at those schools are valuable, and given the Internet, they may be easier to maintain than they were 20 years ago.
