My comment over at Max Bean's:
I think you're giving "grit" too much credit. It isn't clear that it is recognized by more than one psychologist, singular. Nor is it actually one of Seligman’s traditional character strengths. Nor is there any evidence that KIPP is really measuring it in any meaningful way other than simply sticking a number on kids. Nor, for that matter, is the basic finding very surprising -- people that self-report to be focused, ambitious, and persistent are apparently better at sticking with tasks requiring focus, ambition and persistence.