On the other hand, there is already a pretty solid system of private preschools and it would be enormously expensive to try to crowd these out with new public preschools. Since the infrastructure already exists, it makes more sense to give low-income families preschool vouchers to attend private preschools. It would be cheaper and it would result in less segregation by income.
Two issues to respond to here:
1. I heard the Planet Money podcast The Case for Preschool (which is excellent, like most things Planet Money does.) And if pushing to get more poor kids in better preschool programs has good long-term outcomes, then I think Kain's got a good plan for a way to do that. I'm not convinced government needs to be involved with schools at all, so letting the private market do most of the heavy lifting is preferable to a big government system of preschools (which would probably end up a disaster anyway.)
2. I am not convinced we should push preschool. I understand that for kids who aren't getting life skills at home, preschool can be a place to get those. But other research shows that too much school too soon is harmful to long-term outcomes. So universal preschool is not one of my political goals - particularly since I have no intention of sending my own children (someday?) to preschool and would resent having to explain to the government why not.