INDIANAPOLIS - The Indiana Supreme Court on Tuesday upheld the nation's broadest school voucher program in a ruling supporters say could set a national precedent as other states look to build or expand programs that use public money to allow students to attend private schools.

The state's highest court unanimously upheld a 2011 law providing vouchers for low- and middle-income families and cleared the way for an expansion being debated in the Indiana Statehouse. But more importantly, it could settle the case law for other states where voucher programs face legal challenges, supporters contend.

"I think it will be incredibly influential," said Bert Gall, senior attorney for the Washington-based Institute for Justice, who helped defend the Indiana law.

The Indiana voucher program, passed by the Legislature in 2011, is the most sweeping in the nation and the biggest test yet of the conservative Republican idea that giving families choice creates a greater incentive for public schools to improve. Unlike voucher programs in other states, which are limited to poor families and failing school districts, the Indiana program is open to a much broader range of people, including parents with household incomes of up to nearly $64,000 for a family of four.

Jeff Reed, spokesman for the Friedman Foundation for Educational Choice, said 530,000 Indiana students qualify for vouchers, although only 9,000 currently receive them. Public school officials fear the eventual loss of thousands of students, especially those from the middle class, along with the state money that comes with them.

The Milwaukee Parental Choice Program is the nation's largest in terms of actual enrollment. That program, enacted in 1990, had 24,027 participants this school year, Reed said.

The U.S. Supreme Court kicked the fight over school vouchers to the states in a split 2002 ruling, in which conservative members led by then-Chief Justice William Rehnquist said vouchers do not violate the U.S. Constitution's clause separating church and state. That left supporters and opponents to fight over whether school voucher laws violated similar clauses in state constitutions.

Indiana joins states like Louisiana and Wisconsin, where voucher or voucher-style laws have been upheld. But Arizona and Florida's courts have ruled against vouchers, and the issue remains to be resolved in other states.

Supporters say the Indiana ruling could influence courts in other states because the Indiana constitution contains a clause copied by many states in the mid-1800s in an effort to bar public aid for Catholic schools. The so-called "Blaine Amendment" was meant at the time to keep public money flowing to Protestant-dominated public schools.

That means the Indiana ruling could apply anywhere with a "Blaine" law, Gall said.

"For us, and for the Indiana Supreme Court, the Blaine Amendment in Indiana basically prevented spending for the benefit of religious institutions. And the Indiana Supreme Court said `No, this is spending for the benefit of parents and students,'" he said.

Opponents downplayed Tuesday's ruling. Brenda Pike, executive director of the Indiana State Teachers Association and a lead plaintiff in the case, said the group now considers vouchers settled law in Indiana. But, she added, Indiana's borders are where the ruling's impact ends.

"This was a specific Indiana constitutional law question," Pike said. "We went through the court system in Indiana, not any federal court system."

Lawyers for national groups who argued against the Indiana law deferred questions to ISTA on Tuesday.

Solicitor General Thomas Fisher, who defended the law before the state Supreme Court in November, told the justices then that parents were free to send their children to any school they wished, public or private, religious or not.

The court agreed with that, saying in a 22-page opinion written by Chief Justice Brent Dickson that the program primarily benefited parents, not schools, because it gave parents the choice in their children's education.

Dickson also rejected school voucher opponents' claims that the state constitution requires a public school system, saying lawmakers have broad discretion in how children are educated.

State School Superintendent Glenda Ritz joined the lawsuit while campaigning last year but removed her name from the list of plaintiffs shortly after winning office.

"As State Superintendent, I will follow the court's ruling and faithfully administer Indiana's voucher program," she said in a statement. "However, I personally believe that public dollars should go to public schools, and I encourage Hoosiers to send that message to their representatives in the Statehouse."

There is still some question about how popular the vouchers are in Indiana. Voters elected Ritz over former Republican Schools Superintendent Tony Bennett, long the state's most visible supporter of vouchers. But they also awarded a supermajority to House Republicans, who have pushed for a sweeping expansion of vouchers this year.

The expansion bill is awaiting action in the state Senate, where there have been concerns about its cost and whether the Legislature should start making exceptions to the 2011 compromise that then-Gov. Mitch Daniels touted as giving public schools a chance to win over students and parents.

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Associated Press reporters Pam Engel and Tom Davies in Indianapolis contributed to this report.