@engineer,
I have a feeling I have to read a lot more to speak intelligently about this. But re: this last post... When we were trying to figure out where to live in this area I looked carefully at several school districts. There was a district that was mostly white and affluent and had very, very good test scores and lots of extras (languages, etc.). I purposely decided against this district, and chose one that had good test scores (not as good) and significantly more economic and cultural diversity. I think that is important.
In your letter, I think that you're oversimplifying the problem re: teaching and facilities. Peers are very important, too. Studies have shown (I can try to find 'em) that when there is fairly equal mix of high-achieving and lower-achieving students, the high-achieving students continue to do well (they are not significantly negatively impacted) while the lower-achieving students tend to do much better than when they were surrounded by other low-achieving students.
There is a direct peer-to-peer effect (kids helping their peers, which solidifies knowledge for the helper as well as obviously helping the helpee) and also a cultural effect (the value placed on education/ learning in general).