2013-2014 Madison School Board President Ed Hughes:

The proponents of the proposed expansion of Wisconsin’s private-school voucher program have run out of substantive arguments. Governor Walker’s “This is about children” illustrates how vacuous their efforts at persuasion have become.
When Governor Walker’s budget was first announced, his initial talking points in support of his voucher expansion plan featured the claim that schools in the nine targeted school districts were failing and vouchers were necessary to provide a lifeline to students who needed help to pursue other schooling options. Neither the governor nor his supporters are pushing that argument any more. It seems that they got the point that it is not a smart move politically for the governor to go around trashing the public schools in some of the larger urban areas of the state.
While proponents have claimed that students in voucher schools do better academically, the wind has gone out of the sails of that argument as well. DPI has reported that students in voucher schools in Milwaukee and Racine performed worse on the WKCE than students in the public schools in those communities. Voucher school advocates can point to data that supposedly support their view, opponents can counter with contrary figures, and at best the evidence on improved student performance is a wash. There is no reason to think that students in the nine districts targeted for voucher expansion would do any better in the private schools in their area than they would in their neighborhood public schools. No one has offered an argument to the contrary.
Voucher proponents sometimes try to construct a cost-savings argument around the fact that the per-pupil amounts that voucher students would receive are less than the average per-pupil expenditures by their school districts. But this argument goes nowhere because no one is proposing that the public schools shut down as voucher schools expand. Consequently, there’s really not much of a response to the observation credited to former Governor Tommy Thompson that “We can’t afford two systems of education.”
Additionally, voucher schools have not discovered a magic bullet that allows them to educate students across the spectrum of needs more economically. Here’s a telling excerpt from an op ed by the Choice Schools Association advocating for much higher voucher payments and posted on line by the right-wing MacIver Institute:

Vouchers are hardly an existential threat to the Madison School District. Rather, the District’s long term disastrous reading scores are the essential issue, one that merits endless attention and improvement.
2005: When all third graders read at grade level or beyond by the end of the year, the achievement gap will be closed…and not before.