This was originally created as a way to help students in lower income areas achieve the ability to go to a private school. This has never happened, and it never will. Voucher programs instead leave these kids is now grossly underfunded schools while rich tax payers make sure their kids have a well funded, exclusive education. (yay capitalism!).
Alex Morris at Rolling Stone explains it like this:
Georgia, along with 11 other states (Arizona, Pennsylvania, Florida, Rhode Island, Iowa, Indiana, Oklahoma, Virginia, New Hampshire, Louisiana and, most recently, Alabama), has adopted laws – sometimes referred to as "neovouchers" – to grant dollar-for-dollar tax credits to people who donate money to provide children with scholarships to private schools. In theory, such a plan has the potential to help a lot of students, but in practice, especially in deeply religious places like Georgia, it has also meant that millions of dollars have been redirected from public funds to privately run Student Scholarship Organizations, which can then funnel the money to schools with strict anti-gay policies.