COLUMBIA - School-choice advocates said on Thursday that they've found a $98 million reason why South Carolina lawmakers should approve public funding for private-school tuition.

Unsuccessful so far in convincing the General Assembly to pass a school-choice plan, two groups have compiled a report detailing what South Carolina's high dropout rate costs the state and calculating how school choice could help.

"I wouldn't describe this as a new tactic with regards to advocating school choice," Gov. Mark Sanford said. "But it's simply more data on why I think it's relevant and important."

South Carolina's graduation rate stands between about 52 percent and 74 percent, depending on how it's factored.

Regardless, the state consistently ranks at or near the bottom nationally.

About 617,000 public school pupils are enrolled in grades one through 12.

Each year, a new group of dropouts costs the state $98 million in lost tax revenues, increased Medicaid expenses and higher incarceration costs, the South Carolina Policy Council and the Milton & Rose D. Friedman Foundation said Thursday, based on an analysis of U.S. Census data.

But the state could save between $5 million and $10 million of that annually if another 35,794 first- through 12th-grade pupils attended private schools, the groups said.

By increasing competition among schools, the report says, the state's graduation rate would increase 2.4 to 4.8 percent - thereby raising tax revenues while reducing Medicaid and incarceration costs.

"Dropping out not only costs children their hopes and dreams, it costs taxpayers millions of dollars every year and the state thousands of jobs," said Robert Enlow, the Friedman Foundation's executive director.

Legislative support for school-choice plans has been significant at times over the past three years. But despite tweaks and amendments, proponents have not won over a majority of lawmakers.

Still, school-choice advocates point to successes - notably, the approval of state-sponsored charter schools and an expansion of South Carolina's virtual-school program.

Mr. Sanford said he doesn't know what next year's school-choice proposal will be, but he promised: "We'll be back with other ideas on that front."