PHOENIX — Arizona’s schools chief has decided to have state taxpayers pay more to help some children attend private and parochial schools than they would to keep them in public schools.

John Huppenthal, state superintendent of public instruction, announced the decision is based on his new interpretation of state law. It requires those vouchers to be computed based on what the state now pays in per-pupil aid to charter schools, he said.

That aid runs up to $1,963 more than the $3,500 to $5,000 provided on a per-student basis to public schools.

Under Huppenthal’s new interpretation, a student who leaves a traditional public school will get 90 percent of per-pupil charter school funding — an amount that exceeds current state aid for public school students. Under the old interpretation, a student leaving a public school got the smaller figure of 90 percent of per-pupil public-school funding.

The funding change will take effect in the coming school year, Huppenthal said.

Public-school advocates say that violates the statute, and a lawsuit is likely in the works, said Jennifer Loredo, spokeswoman for the Arizona Education Association.

“On first blush (Huppenthal’s) Department of Education is either trying to take a political loophole to advance a political ideology or they’re violating the law. It has to be one or the other,” Tim Ogle, executive director of the Arizona School Boards Association, told The Associated Press.

Rep. J.D. Mesnard, a Chandler Republican who supports what backers call empowerment scholarship accounts, said he agrees with Huppenthal’s interpretation.

But Mesnard conceded the language is “ambiguous.” And he agreed with Loredo on one point: It likely will be up to a judge to decide who is right.

Huppenthal’s announcement Friday comes after he asked lawmakers to spell out in statute that vouchers should be based on charter school aid. That language was struck on the last night of the recently ended legislation session.

What that means, Loredo argues, is lawmakers specifically rejected Huppenthal’s interpretation.

Chris Kotterman, lobbyist for the Department of Education, conceded Huppenthal sought that clarification and didn’t persuade legislators.

“But they also didn’t change it and say, ‘Absolutely not, you’re not doing that,’” Kotterman said.

He said that left a “poorly worded statute” in place, which Huppenthal has interpreted.

His action undermines what had been one of the arguments about giving vouchers to private and parochial school students. Supporters pitched it as a savings to the state treasury, as well as a plan that gives more choices to parents beyond traditional public schools and charter schools.

Mesnard said vouchers still save money for taxpayers overall because state aid covers only a portion of what it costs to educate students in public schools. He said the balance is made up by local residents through property taxes.

Vouchers are available only to students who had been in public or charter schools. And the claim was the treasury would be shelling out only 90 percent of what would otherwise be paid in aid.

Vouchers were originally made available only to students with special needs. That was later expanded to any student attending a school rated “D” or “F” by the Department of Education. The law caps how many new kids can enroll until 2020.

Backers sought this year to expand eligibility to perhaps 80 percent of the 1.1 million students in public schools, only to fall short.