If you're writing a college-tuition check this summer, there may be a backdoor way to deduct a chunk of the payment that's perfectly legal yet utterly underutilized.

The trick is to make a contribution to your state's "529" college-savings plan, as long as it's one of the 26 states (plus the District of Columbia) that give you a tax deduction or credit when you deposit money. Then, simply withdraw the money and use it to pay the college bill.

Veteran users of 529 plans know all about the state tax breaks. But plenty of others don't -- and could benefit from the quick in-and-out. "This makes a lot of sense for wealthy people who don't need to save," says tax partner Bernard S. Kent of PricewaterhouseCoopers, who has advised both individuals and savings plans.

Wealthy or not, however, most anyone who doesn't have a 529 yet can get at least a little something back if they live in the right state.

The 529 plans are best known for their federal tax benefits: Your earnings are tax-free if you use them for qualified higher-education expenses. Though this rule expires after 2010, an extension seems likely.

But those 26 states, plus the District of Columbia, also award a state tax break for residents' contributions to the state's own 529 plan (every state has them). Kansas and Maine go further -- starting next year, they'll give deductions for deposits in any state's plan.

These deductions are generally good immediately. So there's usually nothing stopping you from using the accounts as a temporary parking spot for money on its way to the bursar's office. Tell grandma and grandpa, too, if they want to help with tuition, since they're often eligible for the same tax breaks.

How much might this be worth each year? It depends on your state's tax rate and whether it limits the size of your annual tax break for making a 529 deposit. It could be a high three-digit number per household in New York, or $1,000 in Indiana (starting in 2007). Colorado, New Mexico, South Carolina and West Virginia don't limit the annual deduction. See the chart on page B4 for notes on every state that has a tax break.

To get started, and for an excellent primer on 529s in general, go to savingforcollege.com, click on "529 Plans" then click on "529 Plan Details." From there, click on your state for a summary of the details on its "savings" plans (you don't want the "prepaid" plans for this purpose). Then click through to the state's official home page to learn how to open an account and to get money out later.

A caveat: Use the most conservative investment option if you're keeping money there short-term. Many state officials say they don't like their plans being used just for the tax break, but few try to thwart it. New Mexico is one -- its accounts must be open for a year before you can withdraw money. Michigan limits the tax maneuver, too.

You can't really blame the states, though. All states want residents to start saving early, benefit from compounding and get their tax breaks for 20 or 25 years instead of just four. Still, four is better than none, which is why it may be a good idea to send your tuition money on a detour.

Tuition Tax Break

Some details on state tax breaks from "529" college savings accounts:

Deposit money, then take it out; pay tuition and claim your credit/deduction.

You can usually do this even if the account has only been open for a few weeks.