With Chicago students back in the classroom, Mayor Rahm Emanuel is free to push ahead with a key component in his effort to reform the city's public education system — the aggressive expansion of charter schools.

Although it was never officially part of negotiations over a new teachers contract, Emanuel's charter school push was a factor in the seven-day strike by the Chicago Teachers Union. It made the city a national flashpoint in the debate over whether privately run but publicly funded charter networks are a better formula for success than struggling inner-city schools.

Chicago Public Schools officials expect about 53,000 of the district's roughly 400,000 students will attend charter schools this year, and the number of charters will increase to more than 100. The city is aiming to add 60 charter schools in the next five years with support from the Bill & Melinda Gates Foundation, which is trying to expand charters across the country.

The biggest push for charter schools locally comes from some of the wealthiest backers of Emanuel, including Bruce Rauner, a venture capitalist who regularly advises the mayor. At a seminar of business and political leaders held the same day teachers voted to return to school, Rauner said the strike would only energize reform efforts that he called a "multiyear revolution."

"I think we're going to have a coalescing of interests that's a focus and drive some major change. And there are some plans in the works, some charter community education innovators who are now focusing on Chicago, and I think in the coming years we can innovate," he said.

Experts called the union's stand against privately run networks unique in the United States, where several big cities, including New York, also have pushed charter schools.

"What's different is this is really the first mass movement against that comprehensive strategy" for privatization, said Janelle Scott, an associate professor at the University of California at Berkeley who studies school policy.

Emanuel has infused his public school administration with charter school proponents, who contend that the typically nonunion operations are generally cheaper to run and quicker to embrace new ideas in an environment where budgets are under historic levels of stress.

"The mayor's position is that parents need to have the ability to choose a good school that works best for their child, whether that's magnet, charter, neighborhood, turnaround or military school," Emanuel's office said in a prepared statement. "And every school model, including charters, should be and is held to the same standard for accountability for performance."

The claims of charter networks that they do a better job of educating students while doing it more efficiently are challenged by union members and others who say charters drain resources from neighborhood schools. Across-the-board comparisons are difficult because of a labyrinth of statistics and competing claims by proponents on both sides.

The state, school district, civic groups and charter systems themselves have all issued recent reports loaded with data that make even determining comparable per-pupil spending difficult. The Illinois State Board of Education in its most recent report on charters said each of the 38 charter networks in Chicago is governed by its own board and makes its own decisions on curriculum, staffing and the length of the school day.

Student and school performance

Student test scores are the common denominator in comparing charter schools to neighborhood schools, and the results so far are not a clear victory for charters.

In standardized tests last year, Chicago's 95 charter schools performed only slightly better than the city's 675 public schools, according to state records. Of charter students tested, 76.9 percent met state standards, while 73.9 percent of their public school counterparts met standards.

The state's school report card issued last fall showed that more than two dozen schools from some of the best-known local charter networks, including United Neighborhood Organization, had underperformed against the state's standards.

The group often praised by Emanuel as the best of the Chicago charter groups, the Noble Network of Charter Schools, did keep up with state standards, although it did not reach the level of CPS' elite schools that are allowed to select top students.

Chicago's charters as a whole reported a higher graduation rate for the year ending in June 2011 than CPS did — 73.8 percent to 60.6 percent, according to the state and CPS records.

Charter schools, as well as traditional public schools, can be closed for poor performance.

The school district is moving toward a single accountability system that will require charters and neighborhood schools to meet the same accountability and assessment benchmarks, said CPS spokeswoman Robyn Ziegler.

But critics say charter schools' results may look better in part because the schools practice their own form of student selection by squeezing out students with academic or discipline problems.

For instance, Urban Prep Academy has made headlines because the entire graduating class of the all-boys charter school gained college acceptance three years in a row. But school administrators acknowledge that the 2012 class of 85 boys was half its original size by graduation day, though they say the school works hard to keep troubled students in school.

Either way, supporters say a key upside of the charter experience — and one potential factor in student performance — is strongly enforced standards for student behavior.

"You practiced how you were going to sit in the auditorium. ... At a public school, you just don't have that same high expectation of behavior," said former teacher Sara Brown, who has worked at charter and neighborhood schools in Chicago and is now a curriculum writer for an education consulting firm.

"Kids want structure," Brown said. "They want to come into a classroom and know exactly what to expect."

Costs of education

The allure of charter schools is not just the claim that they do a better job of educating, but that they can do so for less money than the public spends on traditional schools.