Oak Park's pricey homes, Frank Lloyd Wright architecture and array of shops and restaurants generate billions in property wealth, funneling a bounty of tax dollars to its elementary school district.

That kind of local affluence usually means fewer dollars from the state to help cover school bills. But Oak Park Elementary School District 97 also receives millions through a little-known state subsidy aimed at fattening its budget.

Oak Park was among those on the receiving end as Illinois quietly doled out some $6 billion since 2000 to boost state aid for select school districts — many in the Chicago region — that couldn't get more money from property owners because of laws that limit tax collections, the Tribune has learned.

Rolled into the usual state aid sent to districts, the subsidies are all but hidden and have been skyrocketing, starting at $46 million and increasing more than 1,000 percent in the years since lawmakers approved them, state data show. At its peak in 2008, the program cost taxpayers $805 million, with the majority of school districts not getting a penny.

"It is ridiculous," said State Superintendent Christopher Koch. "We can't afford it; it doesn't make sense, and it's not fair to everyone else."

Koch and other critics say the subsidies drain the main pot of state aid that is supposed to be distributed equitably across Illinois.

That state-aid money, more than $4 billion annually in the last several years, has been shrinking amid the state's fiscal crisis. And the subsidies have prompted renewed attention from lawmakers grappling with more potential cuts in education aid.

This school year, the subsidies add up to $502 million for 292 districts, about a third of the state's districts, according to data provided by the Illinois State Board of Education.

The payments often are referred to as "adjustments" to a district's state aid.

To be eligible, school districts have to operate under the state's tax cap laws designed to help control local property tax increases. Of the state's 862 districts, 460 fall under the laws. But not all of them get the subsidies — it all depends on the rise and fall of local property values and a complex state formula that essentially pretends a district is less wealthy than it really is.

That's important because property wealth is key to determining how much state aid districts get. Typically, the less local wealth, the more state dollars per student a district receives.

Chicago Public Schools — the state's most property-rich district, even though most of its students are low-income — gets the biggest subsidy this year, about $283.5 million. To make that happen, the state shaved $36 billion from CPS' property wealth, records show.

Without the adjustment, basic state aid for CPS would have been about $130 million instead of $413.3 million.

Cook County districts as a whole get most of the subsidy money, including districts in more affluent communities such as Wilmette, Evanston, Glenview, Schaumburg and Park Ridge.

Many less financially well-off districts in Cook's south and west suburbs also benefit.

Districts in Will, Kane, Lake, McHenry, Kankakee and DuPage counties get the next highest amounts, according to data examined by the Tribune.

'Relief for the wealthiest'

Local school officials say the subsidies have been a lifeline as districts coped with budget challenges during a tough economy.

Oak Park 97 got the fifth-highest subsidy in the state this year — calculated at $7 million.

"That $7 million is a huge percentage of our budget," said Robert Spatz, vice president of the school board, which oversees a budget of nearly $70 million. "Seven million is 100 staff members."

Without the subsidy, Oak Park's basic state aid would have been $1.8 million instead of nearly $9 million.

CPS officials, facing a $1 billion deficit next year, defend the subsidies as a way to help districts that lose out on local revenues because of tax caps, as well as potential state aid because of the way Illinois distributes tax dollars to schools.

But Tom Johnson, president emeritus of the Taxpayers' Federation of Illinois, calls the subsidy program "property tax relief for the wealthiest districts," specifically "those districts that have grown in wealth dramatically."

The subsidies, he said, depart from the original purpose of state aid — to help equalize school spending, whether a district is property rich or poor.

Johnson served as chairman of the Taxpayer Action Board created in 2009 by Gov. Pat Quinn to examine spending and fiscal reforms. The group encouraged a broad school funding review as well as capping — but not eliminating — the subsidies, given the political challenges.

"Any piecemeal change ... would create immediate winners and losers and impede a proper resolution," the group's report stated.

CPS would lose the most if the subsidies were eliminated, so resistance from Chicago lawmakers would be expected.

And now that school districts are dependent on the subsidies, it would be hard for the General Assembly to take them away, said Jeff Mays, a former state lawmaker and president of the nonprofit Illinois Business Roundtable.

Mays is a board member for Quincy Public School District 172 in western Adams County, which isn't under tax caps and doesn't get subsidies.

"That takes money away from us,'' Mays said.

Shrinking resources

The subsidy formula dates to legislation in the late 1990s, said Rob Grossi, treasurer of the Bloom Township Trustees of Schools, who worked on the original formula.

At the time, districts were realizing the impact of the new tax cap law, called the Property Tax Extension Limitation Law, or PTELL.

The tax-cap law emerged in the early to mid-1990s as property tax bills were skyrocketing and taxpayers were growing fed up. PTELL generally limits increases in overall taxes billed annually to 5 percent, or the rate of inflation, whichever is less. Voters can approve larger increases.

Chicago's collar counties were the first to be subjected to the caps, followed by Cook County. Elsewhere, county voters could decide whether to use tax caps.

Districts facing loss of local dollars discovered that tax cap restrictions could affect their ability to get state aid as well, Grossi said, because of the way a district's property wealth was factored into the state aid formula. More wealth usually means less state aid, so the wealth figure in the formula is pivotal.