“Milton Friedman, the Nobel Prize-winning economist known for his free-market views, proposed 50 years ago that to improve schools, parents could be given vouchers — tickets they could spend to shop for a better education for their kids. He theorized that the resulting competition among schools would spark improvements in the system. Free-market advocates loved the idea. Teachers’ unions hated it, arguing that it could drain resources from some public schools and direct resources to religious institutions.”