Word no sooner leaked out last week that S.C. high-school students racked up the lowest average SAT scores in the nation than the jackals began ripping at S.C. public education.

Gov. Mark Sanford opined that despite a 130 percent, 30-year increase in state support for public schools, this year's SAT performance bolstered his case for more charter schools and state tax credits for parents wishing to move their kids to private schools.

Senate candidate Rep. Jim DeMint, R-Greenville, blasted his Democratic opponent, S.C. Education Superintendent Inez Tenenbaum, for what he sees as ineffective leadership of public schools.

And South Carolinians for Responsible Government, the group lobbying the General Assembly for education tax credits, reiterated that only competition from private schools can goad public educators to perform more effectively on behalf of S.C. schoolchildren.

These folks are feasting on the wrong carcass. SAT average scores say little about school quality - though they speak volumes about the motivation of the youngsters taking the test. That's because:

Too few students in the typical S.C. high school take the SAT to allow average results in a given year to be used as a measure of the quality of the teaching in that school.

Those who take the SAT typically are middle-class youngsters who ought to have taken enough English and math courses to earn respectable, if not outstanding, test scores.

When individual SAT-takers perform below expectations, their teachers might deserve some of the blame. But the more likely problem is the importance or lack of same that individual students attribute to the SAT.

If their college aspirations include selective schools such as Duke, Furman, Wake Forest or Emory universities, they'll work nights and weekends with SAT-preparation books and software to earn high scores. If their higher-ed sights are set lower - the typical state-supported university, for example - they may not work as hard because many schools will admit students with mediocre SAT scores.

Why do South Carolinians get so exercised about SAT results? Back in the 1990s, when politicians of both parties realized S.C. public schools are in need of an upgrade, they selected the SAT as one gauge of how well their school-improvement laws were working.

Bad move. The SAT has never been a valid measure of school improvement.

The only valid S.C. measure of school improvement is the Palmetto Achievement Challenge Test - among the best school-accountability systems in the nation. The PACT measures yearly student progress in science, math, social studies, reading and writing between grades three and eight, then provides a final check in the second year of high school with an exit exam.

The PACT measures how well all students are doing, not just those planning to attend college. It leaves individual educators whose students aren't gaining critical knowledge grade by grade no place to hide (which may be why the school-tax-credit lobby would avoid including publicly supported private schools in the PACT system).

To be sure, S.C. SAT average scores should be higher. But to use this year's scores to condemn the public schools and Tenenbaum as their chief is disingenuous.