Subject: Re: 16% of kids don't speak English
There's a good chance that any parent that can afford private school would send their kids there anyway, no matter what city they lived in.

Not in every city. Here in Miami, and I expect many others, the wealthy parents would use their wealth to buy homes in the attendance districts of the better public schools. Cheaper than private school, since you can (usually) recapture that premium when your kids leave home and you resell the house.