Harry Miley, a former adviser to two GOP governors, has found a huge chink in the armor of Gov. Mark Sanford's proposal to subsidize private-school tuition. Supporters of the proposal, the Put Parents in Charge Act, contend that sending former public schoolchildren to private schools would actually enrich public schools.

As "proof," they offer Clemson economist Cotton Lindsay's 2004 cost analysis of the proposal, which would use state and local tax credits to help parents defray private-school tuition. Lindsay "found" that public schools would gain $600 for each student who leaves for a private school.

But in a new study commissioned by the associations that represent S.C. school boards and school administrators, Miley concludes that the Put Parents in Charge Act actually would cost each S.C. school district an average $4.1 million in the first five years of its life. In his study, Miley takes the harsh realities of the S.C. school finance and school maintenance into account. Lindsay's study did not.

Specifically, Miley and his associates note that fixed public school costs would remain when a student leaves a classroom. Lindsay assumes in his study that so many children would leave public schools under Put Parents in Charge, school districts could shut down entire classrooms. This is highly debatable.

In most S.C. school districts, academic quality, as measured by the state's report card system, continues to improve. Parents who believe that public schools work for their children seem unlikely to exercise a private-school option.

If fewer students are using school buildings, as Miley notes, the buildings still need to be heated, cooled and maintained. Lindsay's assumption would be valid only if so many kids left public schools that entire buildings could be shut down and large numbers of teachers could be laid off.

The most glaring omission from Lindsay's study is the financial pounding that Put Parents in Charge would exert on school districts because of the mechanics of S.C. Education Finance Act - the law with which the state supplements local school funding.

Miley notes that every student who leaves Horry County Schools would cost the school district $938 in state payments. In Georgetown, the Education Finance Act hit would be larger, as that district educates a higher percentage of children from low-income families.

All this, of course, begs the question of whether public schools that parents say are failing deserve to keep their per-pupil appropriations from the state.

But the concern here is the demonstrable weaknesses of Lindsay's 2004 findings.

Put Parents in Charge advocates frequently cite his study to bolster their argument that enactment of state income tax and property-tax credits for private-school tuition would not hurt the public schools. As legislators weigh the merits of Sanford's proposal this year, they at least should work from a reliable set of assumptions about its financial effect on public schools over time.

Regardless of what South Carolinians think about them, public schools will remain the state's main basic-education delivery system if Put Parents in Charge becomes law. Blowing a hole in the public school finance system because of misinformation about the effects of Put Parents in Charge would be foolish public policy.