South Carolina public schools face enough challenges without national special-interest groups interfering.

Two groups are pumping money into the state to promote school vouchers. They are trying to influence the outcome of Statehouse elections this November, and they vow to keep applying pressure to legislators in next year's session.

The Associated Press reports that two groups have spent about $150,000 on ads and direct mailings in South Carolina. One group helped an in-state organization run a phone bank to connect voters with state lawmakers.

Vouchers, or tax credits given to parents of students in private schools or businesses that donate scholarship money for private schools, are a bad idea. Where have the out-of-state ideologues been all these years as responsible state citizens and leaders have worked so hard to pull up public schools in South Carolina through the landmark Education Finance Act, Education Improvement Act and the Education Accountability Act? They've been absent, and that's because their agenda is not to boost South Carolina public schools, but to tear them apart.

South Carolina public schools, like many around the nation, have a lot of hurdles to cross in the drive for excellence. But none of them will be helped by the tax-credit plan pushed by Gov. Mark Sanford and the out-of-state ideologues.

They say public schools would improve because they would have to compete in an open marketplace. That is already the case. Our community has a wide choice of fine private schools. Market competition is bristling, but that does not change the fact that every penny of the public dollar should go to the public schools -- the only ones accountable fiscally and academically to the public.

Voucher proponents talk about competition, but they don't want fair competition. They want to siphon students away from public schools into schools that do not have to take all comers, do not have to force students to take statewide standardized tests, do not have to post test scores and reams of other comparative data to the public, do not have to have teachers subject to rigorous certification requirements and do not have to account for the expenditure of public dollars.

Private schools serve a valid purpose, but so do the public schools. South Carolinians should tell the out-of-state ideologues that the best way to improve public schools is to rally behind them, not encourage the best students and most caring parents to leave them behind.