South Carolina's public schools stand to lose $354 million under Gov. Mark Sanford's plan to provide tax credits to parents who send their children to private school, public school advocates said in a study released Tuesday.

In response, proponents of the Put Parents in Charge legislation immediately assailed the findings as out of date.

The report said that each school district on average would lose $4.1 million if the tax credit were fully implemented in five years.

Like a similar version of the plan last year, "the new bill is still based on diverting state funding," said Debbie Elmore, spokeswoman for the South Carolina School Boards Association, which commissioned the $15,000 study with the state Association of School Administrators.

Sanford's plan would grant parents tax credits or scholarships, depending on their incomes, to offset private school tuition or home-schooling costs.

Tuesday's report, written by Harry Miley, a former economic adviser to Republican Govs. Carroll Campbell and David Beasley, contradicts a 2004 study by Clemson University economist Cotton Lindsay that said schools would save money under Sanford's plan. That study was released by the South Carolina Policy Council, a conservative think tank that supports school choice.

Miley concluded that instead of school districts saving $600 per migrating student, districts would lose between $570 and $2,040 per student because more money may be spent on special-needs or gifted students.

"Faced with shortfalls from declining enrollment and the pervasiveness of fixed costs, schools would require more money precisely at the moment that state and local coffers are emptied by the tax credit," Miley said.

"If legislators and other policymakers fail to anticipate the impact of the foreseeable and likely negative consequences of such legislation, unfortunately the onus and ultimate impact of fiscal harm will fall upon South Carolina's children," he said.

Miley concluded that the Policy Council study was flawed. Basing important policy decisions on its findings "would be a profound mistake," he said.

School Boards Association President Porter Stewart echoed Miley's warning and dubbed the tax credit proposal the "Education Abandonment Act."

"We cannot afford ... to publicly fund two systems of education in South Carolina -- a public one and a private-religious one," he said.

State Education Superintendent Inez Tenenbaum agreed.

"This school voucher bill is bad public policy, pure and simple," Tenenbaum said. "It's unproven, unaccountable and unaffordable."

Ann Ashley of Summerville's New Beginnings Home School Association called it a way for the wealthy to fund private schools. "They are trying to take my tax dollars to educate the upper class," she said.

Policy Council President Ed McMullen fired back, calling the study's backers "a group of political hacks who have no idea how economics pertain to education."

McMullen added, "Miley and the school administrators can manipulate facts, but they cannot change the reality that half of our freshmen do not finish high school, and three-fourths of our eighth-graders cannot read at a proficient level.

"We need to care more for the children than the system and be motivated more by what is best for them than by the fear of change that is driving a few education administrators," he said.

Lindsay defended his findings, saying Miley's concern is unfounded because student migration will not be uniform across every grade in every school.

"Those where students are unable to learn will find their enrollments shrinking and not by only five pupils per classroom, but by whole classrooms," he said.

Lindsay plans to release an updated report that addresses district-by-district concerns, since districts' funding is not equal. For instance, Horry County School District received $938 per student in 2002-2003; Hampton 2 got $1,641.

The governor's office also weighed in. "We have a great deal for the current education bureaucracy: It can keep over two-thirds of the $9,800 that it spends attempting to educate each child and we will give parents access to the marketplace with the other third to make sure that somebody is actually educating that child," Sanford spokesman Will Folks said.