M. Spencer Green / AP

Parents of Chicago public school students, Carmen Brownlee, left, and, Latonya Williams, right, walk a picket line outside Shoop Elementary School in support of striking CPS teachers, Sept. 11, 2012.

With negotiators trying to hammer out an agreement that would end Chicago’s teachers strike, one of the key sticking points is how to evaluate whether a teacher is doing a good job, an issue that has riled school boards across the U.S. in recent years.

Chicago’s school leaders are proposing that student performance on standardized tests count toward 25 percent of a teacher’s assessment, growing to 40 percent in five years, according to NBCChicago.com.

But Chicago Teachers Union President Karen Lewis is critical of Mayor Rahm Emanuel’s push to make great use of standardized tests in teacher reviews, calling the process flawed. Union officials say the system wouldn’t do enough to take into account outside factors such as poverty, crime and homelessness.

"Evaluate us on what we do, not the lives of our children we do not control," Lewis said in announcing the strike. It was unclear what union officials proposed instead.

The battle in Chicago over using student test scores to judge teachers is just one front in a nationwide battle over how to make sure teachers are doing a good job, and that taxpayer dollars and student time aren’t going to waste.

"This is going to become a long-term battle that everyone's watching very closely," said Eric Hanushek, a senior fellow in education at the Stanford University’s Hoover Institution, a conservative research center. "Teacher unions are at a crossroads: Are they going to participate in designing better teacher evaluations or resist and not change anything. The Chicago union seems to be taking the resist option, drawing their line in the sand."

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The Obama administration, through its $4 billion Race to the Top competition and waivers from the Bush-era No Child Left Behind, has urged states to change teacher assessments to make use of test data as a key component to set a teacher's pay or end their employment. The administration granted waivers to states that promised to show improvements in student and school performance and link teacher evaluations to student test scores.

Supporters say current review tools fail to give administrators a reliable assessment of a teacher's effectiveness, while critics argue there's no evidence linking student performance to a teacher's worth.

"Teacher evaluations should be based on multiple measures," said Marcus Mrowka, a spokesman for the American Federation of Teachers, which has 1.5 million members. "Testing has a role but should not sanction teachers but inform instruction."

Twenty-four states now require teacher evaluations based on some measure of student growth, according to an analysis by the National Council on Teacher Quality, a research and policy group. Public school districts in Tennessee and Washington, D.C., recently implemented new teacher evaluations tying outcomes to merit raises, while Colorado and New York are deep in the process of developing an evaluation system, the council noted.

In the past three years, at least 20 state legislatures have passed bills setting up new teacher evaluation processes, according to the council. Illinois joined the ranks last year when its legislature passed a law mandating new teacher evaluations, with Chicago’s leaders rushing to embrace the system, called the Performance Evaluation Review Act.

“The evaluation system should be built around continuing improvement of instruction,” said Rob Weil, AFT’s director of field programs and educational issues in Washington, D.C. “Evaluations should help people improve and we need to build systems that give teachers the information they need so they can improve. The process should not be punitive.”

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In Chicago, Lewis has warned that as many as 6,000 teachers could lose their jobs under the new evaluation system. The union represents about 25,000 teachers and staff, who walked off the job Monday.

School officials say they do not know how union leaders determined that number, and telephone calls by NBC News to union headquarters went unanswered Tuesday.

Emanuel has promised that teachers would not be fired in the first year of the evaluation process.

Union leaders, however, are still resisting.

“This is no way to measure the effectiveness of an educator,” said the union in a statement. “Further there are too many factors beyond our control which impact how well some students perform on standardized tests such as poverty, exposure to violence, homelessness, hunger and other social issues beyond our control.”

About 60 percent of students in Chicago public schools complete high school, according to the Illinois Policy Institute, a nonpartisan think tank. 

“We are spending more and more on students, throwing more and more money into the system,” said Ted Dabrowski, vice president of the Illinois Policy Institute. “If you want the best teachers in the system, then teachers should be paid and promoted based on their performance. It’s important that we improve the system, which has become a failed system.”

Do you have an education-related story? Contact Sevil Omer at sevil.omer@msnbc.com

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