The constitutionality of school voucher programs under the U.S. Constitution has been long-established, under the 2002 case known as Zelman v. Simmons-Harris, which arose out of a program in Cleveland, Ohio.
Arizona takes a different approach: Donate to an organization that gives scholarships that students can use to attend a private school, and you get a tax credit. The organizations are called “student tuitioning organizations,” as you might expect, they’re a hit with both donors and the families that benefit from the resulting scholarships. Since Arizona adopted this approach in 1997, Florida, Georgia, Indiana, Iowa, Pennsylvania, and Rhode Island have followed suit.
The ACLU and others have challenged the constitutionality of the Arizona program, saying that it creates an establishment of religion. Some students use the scholarships at religious schools.
The Court will hear oral arguments in October, and deliver its opinion in May or June, 2011.