I think it's Politico that has an article on the one voucher system that's worked pretty well.  That would be in New Orleans after Katrina.  One of the reasons for the success is there was no coherent public school system left and so they were able to invent a joint system.  It also took a lot of re evaluating the original concept that included adding serious accountability standards for Charter Schools.  The accountability standards weeded out the "Jim Bob Evangelical Jesus' schools for academic failure.  The Charter School voucher system pushed by De Voss in Michigan is not working out nearly so well.