A new study reaches a very heartening conclusion. Despite all the brickbats hurled at the Chicago Public Schools over the past 30 years, student achievement in these schools is the best in the state, when compared to similar students.

There has long been a perception that Chicago, like other big-city districts, has dismal academic performance.

But the new study matched students by race and income and discovered that Chicago students outperform kids in the rest of the state.

This is true for African-American students, white students, and Latino students, whether they are low-income or “non-poor.”

“You name the subgroup, and kids in Chicago are doing substantially better than other Illinois kids outside the city,” [Paul] Zavitkovsky said. A similar analysis by the University of Chicago’s Consortium on School Research in 2007 had similar findings but never got much attention.

Chicago also has seen significant growth in its graduation rates and in average scores on the ACT college entrance exam.

The UIC study also documents the impact of expanding poverty in suburban and downstate districts. Fifty percent of Illinois public school kids now qualify for free and reduced price lunch, up from 37 percent in 2001. And while most low-income children in the state were at one time enrolled in Chicago schools, two-thirds now live outside the city — and that number is growing.

Zavitkovsky’s key finding: Poverty is an “equal opportunity disruptor.” In suburban and downstate districts where poverty rates have gone up — in many cases by double digits — test scores have faltered or been stagnant. Researchers long ago established that poverty drags down scores.

The author, Paul Zavitkovsky, told NPR:

The household income of a youngster predicts pretty clearly, if you look at averages, how a student is going to do, with remarkable accuracy.