Indiana lawmakers will start the debate Tuesday on the most controversial plank of Gov. Mitch Daniels' sweeping education platform: a plan to use taxpayer money to help parents send their children to private schools.

Republican lawmakers who control the House and Senate have been successful so far in their efforts to shepherd Daniels' education proposals through the legislative process despite objections from many teachers, education unions and minority Democrats. But the voucher bill, which will be debated in the House education committee Tuesday, seems to be raising the most questions.

Opponents are criticizing the proposals' basic principle — shifting public money to private schools — and some lawmakers have more practical concerns that supporters hope to address by amending the bill Tuesday.

"I think there are more questions about this bill among lawmakers than some of the other (education) proposals," said House Speaker Brian Bosma, a Republican from Indianapolis who is one of the bill's sponsors.

One of those is exactly who should qualify for a voucher, which supporters including Bosma have dubbed "school choice scholarships."

Under the plan, money that would typically go to a public school for educating a child would be given to an eligible parent to use at a private school instead. The state won't give parents the entire amount that would have gone to the public school, however, which could mean the state could save money through the program. Only students currently in public schools would be eligible.

The bill uses a sliding scale that gives the most needy families larger vouchers worth 90 percent of the per-student amount that the student's public school receives. For example, if the state now gives about $6,000 to a public school district for a child's education, it could offer low-income families vouchers worth 90 percent of that, or $5,400. The family could use that toward private school tuition, while the state would keep the remaining $600.

Under the proposal, families that qualify for the federal free or reduced lunch program — those making about $40,000 a year for a family of four — would be eligible for a 90 percent voucher. However, the sliding scale provides 25 percent vouchers — worth about $1,500 in the example situation — for families of four making more than $100,000 a year.

Bosma said supporters hope to tweak the bill to tighten eligibility requirements to focus on lower-income families.

Daniels says it's a matter of justice that low-income students should have the same choice to attend private schools as wealthier families. He and other advocates say Indiana could lead the nation by creating a wide-reaching statewide voucher program.

"We intend to become the first state of full and true choice by saying to every low- and middle-income Hoosier family, 'If you think a non-government school is the right one for your child, you're as entitled to that option as any wealthy family; here's a voucher, go sign up.'" Daniels said in a speech at the Conservative Political Action Conference in Washington, D.C. on Friday.

Public school teachers have denounced the voucher proposal, saying it is part of Daniels' agenda to erode public education. The Indiana Coalition for Public Education held a news conference Monday saying taxpayer money shouldn't be directed to private schools, which can deny admission to certain students and don't have to follow the same accountability rules as public schools.

"By providing vouchers for private schools, we are diverting public tax money to private schools," said Joel Hand, the group's executive director. "That is not taxpayer-friendly to our Hoosier citizens and it is not good policy."

Hand said vouchers blur the line between separation of church and state. He also noted that private schools can deny students admission, and he feared the bill would reverse the state's progress on desegregation efforts.

"Public schools are open to all," he said. "Private schools get to pick and choose."

Hand suggested that the bill could be found unconstitutional, but Bosma said constitutional lawyers have reviewed the proposal and assured him it would stand up in court.

If Daniels' previous education proposals — including bills to limit teachers' collective bargaining, expand charter schools and implement teacher merit pay — are any indication, Tuesday's debate could go on for hours as lawmakers work on details and opponents and supporters voice opinions.

"It should be a robust discussion," Bosma said.