What nobody has mentioned on any of these voucher threads is the programs in place in Florida and now Pennsylvania. Basically, the state gives tax credits (I'm pretty sure it's credits and not deductions) to businesses, who then donate to or set up scholarship funds. These scholarship funds can then be distributed to individuals, who choose the schools that their children will attend.
Avoids all these nasty Constitutional questions, drains $$$ from overbearing government, and allows parents to choose the education they want for their children.
Why, in a free country does one have to go through convoluted schemes when it is such a simple fairness issue? The taxpayer who doesn't use the public schools should be refunded the money he paid for the support of the public schools.
Arizona has credits as well. Vermont and Maine have hundreds of years experience in choice. It works.