Mayor Rahm Emanuel and other city leaders have long heralded charter schools' innovative approach to education, but new research suggests many charters in Chicago are performing no better than traditional neighborhood schools and some are actually doing much worse.

More than two dozen schools in some of the city's most prominent and largest charter networks, including the United Neighborhood Organization (UNO), Chicago International Charter Schools, University of Chicago and LEARN, scored well short of district averages on key standardized tests.

In two of the city's oldest charter networks, Perspectives and Aspira, only one school — Perspectives' IIT Math & Science Academy — surpassed CPS' average on the Illinois Standards Achievement Test, taken by elementary schoolers, or the Prairie State Achievement Examination, used in high schools.

At Shabazz International's DuSable Leadership high school on the South Side, just 7 percent of students met state standards on the PSAE. A few miles south, nine out of every 10 students at CICS' Hawkins high school missed the state benchmark.

The dismal numbers are part of a new set of school report cards the state is releasing to the public Wednesday, results sure to reignite the debate over education reform one day before Chicago Public Schools is expected to release its long-awaited list of school closings for next year.

Andrew Broy, president of the Illinois Network of Charter Schools, acknowledged that maybe a dozen underperforming charter schools are in need of "substantial actions" that may include closing. But simply looking at how many students have met state benchmarks is not a fair assessment, he said; a more important indicator is student growth over time.

"We're in this business because we want to prove that public schools can work," said Juan Rangel, president of the politically connected UNO charter network, which operates nine schools in CPS and plans to open three more next year.

Addressing the failures at UNO's lowest-performing school, Paz Elementary on the West Side, Rangel said: "We're at a point where it's do or die. We're either going to put Paz on course … or we'll have to consider whether this is a school we should keep open."

Two years after Illinois lawmakers approved a more thorough accounting of charter school performance, the state has released data that will allow the public for the first time to see how individual charter schools are measuring up against traditional public schools.

The report cards are somewhat limiting, only looking at a school's performance in 2010-11. But the trends show that despite their celebrated autonomy, discipline and longer school days, charter schools are struggling to overcome the poverty that so often hampers underperforming neighborhood schools.

Charters with the highest numbers of students from low-income families or those with recognized learning disabilities almost universally scored the lowest last year on state exams, a trend common throughout CPS.

One exception is the performance of high schools within the Noble Street Charter network, often touted by Emanuel and others as some of the best charters have to offer. Report cards show Noble students did not reach the level of CPS' elite selective enrollment or magnet schools on the PSAE, but did score on par with state averages — a notable feat for any school in CPS.

But even charters' staunchest supporters admit that success has not been widespread across all schools. New Schools for Chicago, which invested in dozens of charters after then-Mayor Richard Daley launched a massive charter expansion program in 2010, has compiled a watch list for poor-performing charters that they've turned over to CPS.

"In general for charters that have been around for more than five years and not performing, we're supporting their closure or restructuring of these schools," said New Schools Chief Executive Phyllis Lockett. "At the end of the day, we need the bar set on what achievement needs to look like."

Over the last decade, the number of charter schools, which are publicly funded but have relative freedom in decision-making, has grown to 110, and they have become a force in Chicago's crowded public school system.

A report to be released Wednesday by the Brown Center on Education Policy at the Brookings Institution ranks CPS second among large urban districts in providing choices for parents aside from traditional neighborhood schools. Expanding those options is a major point of emphasis for Emanuel and CPS chief Jean-Claude Brizard.

But the majority of charter schools in Chicago and around the U.S. rely on nonunion teachers, who are frequently paid lower wages and asked to work longer hours. That has led to friction with powerful teachers unions, who accuse charter networks of devaluing the profession by driving down salaries and of stripping public money from long-standing neighborhood schools.

"Charter schools, quite frankly, have shown no innovations in instruction," said Chicago Teachers Union President Karen Lewis. "The only innovation they have is in labor management where they can afford to pay a significantly lower amount to their teachers."

Whatever their flaws, charters have a unique advantage over other public schools in their ability to make wholesale changes quickly at schools dogged by poor performance.

Paz has replaced its principal and about 50 percent of its teaching staff and lengthened its school year by 17 days in the last two years, Rangel said. Chicago International Charter, which oversees 16 campuses in CPS, last year removed the management organization responsible for day-to-day operations at five schools.