The first results came in late 2015. Researchers examined an Indiana voucher program that had quickly grown to serve tens of thousands of students under Mike Pence, then the state’s governor. “In mathematics,” they found, “voucher students who transfer to private schools experienced significant losses in achievement.” They also saw no improvement in reading.
https://www.nytimes.com/2017/02/23/upshot/dismal-results-from-vouchers-surprise-researchers-as-devos-era-begins.html?smid=tw-nytimes&smtyp=cur&_r=0