Gov. Mark Sanford says securing state tax credits for parents who want to send their kids to private schools is one of his top five priorities for the remainder of his term. Fair enough.

Long before he became governor, Sanford espoused the truism that forced competition with private schools improves public schools. He is entitled to make that belief a cornerstone of his agenda for the state.

But, as part of his push to persuade the General Assembly to adopt a bill to that effect, Sanford owes S.C. taxpayers the chance to determine whether this truism really is true. He can do that by insisting that the bill - the Put Parents in Charge Act - require private schools that accept tax-credit money to be part of the S.C. school-report-card system.

S.C. legislators set up that system in the late 1990s in response to complaints that public schools were absorbing large sums of state and local tax money while getting poor academic results. The system's purpose, in short, was to establish accountability for public schools.

As part of that, the state initiated the Palmetto Achievement Challenge Tests in reading, writing and math for students in grades three through eight. The idea was to provide educators, legislators, parents and others with an interest in school quality a way to track students' progress in these critical subjects.

More recently, the state has added science and social studies to the PACTs. An exit examination that students take in their second year of high school also has become part of the system - the idea there being to give teachers two years before graduation to help students who fail or score below basic in the critical PACT subjects.

Experts rate the S.C. report-card system one of the best school accountability systems in the nation. Since it works so well for public-school students, why not require private schools that accept students supported by public tax credits to become part of the system, too?

Put another way, since the Put Parents in Charge Act is aimed at establishing a healthy competition between public and private schools, why not ensure that it's a real competition?

The version of the bill introduced in the 2004 General Assembly assumed that parents' satisfaction with publicly supported private schools would be measure enough of the tax credits' success.

That "standard" is fine for schools at which parents pay the cost of tuition out of their own pockets.

But Sanford and other supporters of Put Parents in Charge are asking S.C. taxpayers to make up more than $234 million that would go to tuition tax credits over the program's first five years. In return for a public subsidy that generous, it would be reasonable for S.C. taxpayers to expect a demonstration that their money is being used to good effect.

The report-card/PACT system provides a ready-made tool for public- to private-school comparisons. As part of his push to pass the Put Parents in Charge Act, Sanford should urge lawmakers to include the system in the bill. What better way to demonstrate that the bill really is about school improvement and not, as some charge, about providing underserving parents an unearned subsidy while also weakening public schools?

What better way for Sanford to persuade skeptical South Carolinians that he supports academic superiority, whether delivered to youngsters publicly or privately?