Here's the one trouble. It seems that demographics make more of a difference than public or private school in achievement.
http://www.nytimes.com/2006/01/28/ed...n/28tests.html
Now I'll get the usual backlash out of the way beforehand. Yes, it's a government-financed report. Yes, it's in the NY Times.
I don't think it actually shows that public schools are doing better and I think vouchers might (note that I say might) have a positive effect. But what the study does show is that a parent's preparation and help for the kid, as well as the living environment, is more important than the quality of the school. As such, I don't believe vouchers will do much for the bulk of those oming from poor families unless they are paired with more personal tutoring and help for the parents in parenting skills.
It can't be discounted that most poor and working class families 1) don't understand how college works or how to prepare their kids for it, 2) use authoritarian parenting styles that often set kids up for working class mentality and at extremes can make kids socially underdeveloped and even violent, and 3) if a parent never learned how to do something like calculus, he/she cannot help the kid very well with advanced class homework.
The trouble I have with voucher support is just that some people seem to believe that it will be a magic cure for the education system. People often ignore that schooling is only part, and not so large a part as we think, of a child's eductation and intellectual development.
Unless we help poor parents, we are not going to do much good for poor kids.