COLUMBIA, S.C. - South Carolina school districts would be able to spend more money on each student if a legislative proposal to give tax credits to parents whose children attend private schools is implemented, according to a study released Wednesday by a conservative Columbia-based think tank.

It's the latest study to try to determine the economic impact of the tax credit bill that Gov. Mark Sanford says will give parents more control over their children's education.

Also Wednesday, opponents to the tax credit bill announced the formation of Choose Children First, a coalition of business and community leaders created to defeat the measure.

The impact study by Clemson economist Cotton Lindsay revises estimates from a study Lindsay did last year that was released by the Policy Council and the Legislative Education Action Drive Foundation, a national advocate for school choice.

The new study estimates that school districts across the state would have an extra $1,400 per student in federal, state and local money if the tax-credit plan were fully implemented over five years.

The idea is that when a student leaves, the tax credit proposal only allows him or her to take a portion of the state funds that the school would normally receive. Federal and local dollars are untouched, leaving that money to be divided among fewer students, according to the study.

Lindsay's findings are in stark contrast to those in a study released in February by the South Carolina School Boards Association. That study was written by Harry Miley, an economic adviser to former Republican Govs. Carroll Campbell and David Beasley. Miley's study found that each school district on average would lose $4.1 million if the credit was fully implemented in five years.

Lindsay said his new study's estimates are based on a new version of the tax credit bill introduced last week. The revised bill allows parents to receive smaller tax credits.

The new study also estimates that nearly 105,000 students would leave public schools, up from 42,000 in an earlier study Lindsay did. The new number represents about a sixth of the students now in public schools and twice the number of students now enrolled in independent schools.

"I still find it hard to believe that students will be saving money with the head-count reduction," said Miley, who noted he had not seen the revised study. "I also find it hard to believe that that many students would be migrating out."

State Education Superintendent Inez Tenenbaum said the study still has the same flawed message that public schools would save money with the tax credit. "It really is no different from the original study," Tenenbaum said.

Schools receive state and federal funding based on the number of students enrolled in class, she said. "It shows they don't understand school finances," Tenenbaum said.

School officials also have said the fixed costs of providing an education - which include transportation, utility bills, staff and faculty salaries - don't change when a few students leave the classroom. Miley's study said the schools would have to see large numbers of students leaving to force the departure of teachers before savings can be seen.

Lindsay said his numbers are based on existing state data about cost savings when students leave schools. School district superintendents are good at finding ways to cut costs without cutting personnel when students leave, Lindsay said.

For example, a district superintendent might move a teacher at a school losing students to a more crowded one. Cost savings can't be evaluated on the basis of "one teacher in a classroom or a light bill," he said.