One could theorize that KIPP might not have been able to achieve the same results with a demographically similar group of students with parents who didn't give a damn. Maybe. And maybe, as Rich suggest, KIPP's results are further enhanced by students who can't handle the rigor and move back to other schools. But even if those things were true, so what? Nobody else was stepping up back in 2001 to help those students.
One very simple way to test the "Nobody else was stepping up back in 2001 to help those students" claim Carey makes is to read Jay Mathew's book, a review of which is the impetus for Carey's post. In the book, do our protagonists run into many teachers and administrators who are, in 2001, stepping up to provide a rigorous education for disadvantaged students? Yes! Do they not only find funding for their work, but find it from funders with a long track record of funding the same kind of methods? Yes! Does administration in multiple cities support their efforts and have a portfolio of similar projects? Yes! Most of their battles with administration is over space, which is genuinely constrained in an urban school district that's already loading students into portables.