Since 1982 the Rehnquist Court has been handing down a number of decisions that have lowered the wall of separation. In 1997 it overturned an earlier decision that prohibited public school teachers from providing remedial instruction to students in parochial school facilities. Last Spring a 6-3 majority approved a law that provided assistance, in the form of computers and equipment, to religious schools. A school voucher case pending in an appellate court in Ohio is likely to make its way to the Supreme Court for a clear ruling within the next year or two. JV - Not at all.
Many states have restrictions within their own constitutions that prohibit such plans.
These state constitutional provisions will need to be amended, plus legislative action would be required in the various state legislatures. There is great opposition to choice from those who benefit from the existing government monopoly in education. It can only happen if parents demand to have control over the education of their children. And this demand must be communicated to their legislators and governors.