As far as I know, there are no real criticisms of this program specifically yet. Most of what I have read from about KIPP comes from Paul Tough, both his series of NYTimes Magazine articles and also his book Whatever It Takes. He's clearly a supporter of KIPP, but in his book he also briefly acknowledges that the ideas underlying the program are not supported by science, unlike many recent initiatives to improve parenting ability. (IIRC the school he writes about in the book is not run by KIPP, but it uses their methodology.)