Paul Tough (the NYT's main KIPP advocate) has an article here explaining it:
http://www.nytimes.com/2006/11/26/magazine/26tough.html?_r=0
The basic idea is summed up in this quote from the article: "Can the culture of child-rearing be changed in poor neighborhoods, and if so, is that a project that government or community organizations have the ability, or the right, to take on?" In other words, kids need to be in school 24/7 in order to "change their culture."
There a variety of problems with this, e.g.
- Not supported by data.
- Not being allowed to do stuff on your own prevents you from developing executive function.
- The program revolves entirely around extrinsic motivation, which will prevent most of these kids from actually maturing into adults and being able to handle anything beyond minimum wage jobs.
- Even if these kids do have improved reading and math scores on standardized tests, which there is not yet data to support, it's nowhere near clear that this would outweigh the other problems with the program.
KIPP makes a lot of sense if your goal is to take kids who would normally join gangs and give them enough skills to work at McDonald's, but as a compulsory government program (where you go to prison and literally become a slave if you don't participate) I think this is highly dubious.