The study, conducted by Harry Miley, a former economic adviser to Govs. Carroll Campbell and David Beasley, said school districts could lose an average of $4.1 million in each of the first five years the plan is implemented.

The loss would occur as public school pupils cashed in vouchers to flock to private and home schools and took state funding with them.

The governor's office said the findings were exaggerated and that the plan would actually leave two-thirds of the $9,800 spent on each pupil in the public school system.

"South Carolina is at the bottom of the heap nationally with respect to education, and America is near the bottom compared to the rest of the world," said Will Folks, the governor's spokesman. "The only time we've showed even slight improvement is when we tried something different, specifically, accountability."

The study by Mr. Miley, who is president of a Columbia-based economic consulting firm, counters a 2004 study by Clemson University professor Cotton Lindsay, which said public schools would be better off financially with fewer pupils.

The governor's plan also lacks support from some educators.

State Education Superintendent Inez Tenenbaum is among the critics. She said the proposal is "bad public policy" and encouraged lawmakers to look at Mr. Miley's study.

The South Carolina School Boards Association also opposes the tax credit bill, which is under review by the House Ways and Means Committee.

"In the end, what's really wrong is that (the bill) sends a message that it's okay to abandon public schools, and the state will even give you a financial incentive if you do," said Debbie Elmore, the spokeswoman for the association. "A tax credit is not going to solve those issues and challenges that exist in many of our struggling schools."

Reach Karen Ethridge at (803) 648-1395, ext. 109, or karen.ethridge@augustachronicle.com.