Matthew Yglesias has a post up about Excel Academy in Boston, a charter school which--like KIPP--takes the brightest students from inner-city schools and requires family commitment contracts. Not surprisingly, it gets good results. Yglesias concludes that poor kids need more and better instruction without confronting the fact that the schools "cherry-pick" students.
He's right--more and better instruction is important. Yglesias's commenters point out that the problem isn't as much with academically capable kids from the inner city, but with those with families that don't know or don't care about a good education. Also true. (Note Finland's secrets to success).
Where I taught elementary, one of my colleagues who taught Vanguard (the gifted-talented kids) was perpetually frustrated by KIPP, which tried to recruit her brightest kids. Her feeling was that she'd rather have the kids in public magnet schools than KIPP, which she thought was needed for the kids who might not have been as naturally bright, but were still academically oriented. I tend to agree. Meanwhile, there's still the issue of behavior problems disrupting everyone left behind.