“After just a few years, voucher students perform as well or better than their non-voucher peers while using significantly less public funding,” 

Joanne Jacobs:

Louisiana students who used vouchers to switch from public to private schools did worse in the first year, then improved, concludes a University of Arkansas study. After three years, voucher students were doing as well as similar students who hadn’t switched; low performers did significantly better in English.

The Indiana study looked at students in grades 3-8 who switched from public to private schools. In the first year, they lost ground in math, but they bounced back in the next few years and moved ahead in language arts in the fourth year.

“Overall, voucher students are lower-achieving students from the public sector and enter private schools substantially behind their private school peers, researchers wrote. “During the [Indiana voucher program’s] first few years of implementation, many private schools lacked the capacity or experience in educating new students who are academically behind.”

More, here.

Compare Madison’s spending to voucher schools.