When the voucher program was audited back in 1995 by the University of Wisconsin it was a failure...so the Wisconsin legislature knocked out provisions of the law calling for future evaluations.
http://www.pfaw.org/pfaw/general/default.aspx?oid=1522The program has been riddled with fraud...
http://www.weac.org/News/2004-05/dec04/voucher.htmhttp://www.weac.org/News/2003-04/july04/seppeh.htm"Meanwhile, Alex's Academics of Excellence received $2.8 million in voucher money over three years before the Milwaukee Journal Sentinel reported that the school's founder, James A. Mitchell, served nearly a decade in prison for a 1971 rape. Unlike their counterparts at public schools, principals and teachers at private schools do not have to undergo criminal background checks. "
http://reclaimdemocracy.org/articles_2004/milwaukee_voucher_thieves.htmlAlso worth noting that vouchers have been offered on referendums to voters in at least nine states and have been rejected in all of them by ever increasing margins.