It's 10 days until the end of the year and Illinois still has nothing to replace the stopgap budget that expires on December 31. Bruce Rauner has drawn a relatively hard line, insisting that Democrats approve term limits and a property tax freeze in order to get a new stopgap budget.

I've written before about term limits: while they seem like a not-great idea on the whole, the effects also seem marginal enough that the idea could be a good trade chip. But a property tax freeze could have dramatic, immediate impacts. In August 2015, when the idea was floated, the DeKalb school district said that it would lose $670,000. District 115 in Lake Forest estimated it would cost them $1.6 million over two years, equivalent to "10 or 12 teachers." (Rauner's proposal wouldn't necessarily eliminate property tax increases for good. Home-rule municipalities could be exempt, and either way, any municipality could hold a referendum to raise property taxes.)

But the freeze could lead to unexpected benefits, if it changes the way Illinois funds its schools.

Right now, Illinois is a relatively low-tax state that puts a low percentage of state money toward education—the lowest in the country, and less than half the national average. Local property taxes tend to pick up the slack; as Diane Rado reported for the Trib a couple months ago, local funding makes up 67 percent of school funding in the state, up more than five percentage points since 2001. In wealthier districts, local funding sometimes provide more than 90 percent of total funding.

The result? Illinois has the country's largest funding gap between low-poverty and high-poverty districts, according to last year's Education Trust analysis. We're also an extreme outlier: the highest-poverty districts in Illinois get almost twenty percent less funding than the lowest-poverty districts, a disparity that is twice as big as the second-worst state. And with the state's fiscal problems, cuts hit more state-dependent—i.e. poorer—districts harder.

There are a lot of reasons a property tax freeze could be problematic, not least that its effects are seemingly unpredictable. The most fearsome of possible outcomes is underfunded schools, considering how much districts rely on property taxes. But the freeze could also mean Illinois will rebalance its school funding, something Rauner himself suggested last year: "We're going to give more state support for education" he said. "That eases up on the property tax burden."

Recent studies highlighted by Kevin Carey and Elizabeth A. Harris in the New York Times show how school finance reform can increase education funding for all districts, especially in low-income areas, while improving student outcomes. That was the case in a new paper co-authored by Northwestern's Diane Whitmore Schanzenbach. Researchers calculated that for every $3,400 in additional spending per student over 10 years, adults could expect to see a $5,000 bump in earnings (a calculation based on increased test scores)—an almost 150 percent return on investment based on income increases alone.

The other evidence is from a study led by Northwestern's C. Kirabo Jackson, which looks at similar increases in per-student spending, on a longer timeframe, and with a broader set of measured results. They found broader gains, strictly for low-income students. For every 10 percent increase in per-student funding over 12 years, they completed roughly an additional half year of education, earned 9.6 percent more money, and saw a 6.1 percent reduction in annual incidence of adult poverty. 

To put these results in perspective, the education gap between children from low-income and nonpoor families is one full year. Thus, the estimated effect of a 22 percent increase in per-pupil spending throughout all 12 school-age years for low-income children is large enough to eliminate the education gap between children from low-income and nonpoor families. In relation to current spending levels (the average for 2012 was $12,600 per pupil), this would correspond to increasing per-pupil spending permanently by roughly $2,863 per student.

The property-tax freeze is an odd idea in some ways, especially in that it shifts the hard parts of making the state more competitive and attractive onto towns and cities, taking away a considerable degree of autonomy and local control. But in the specific matter of school funding, that might not be a bad thing for the state as a whole.