Over 30,000 public school teachers in Chicago went on strike on Monday. High among their grievances was the increasing prominence of standardized test scores in teacher evaluations.

The teacher strike, the first in 25 years for the nation's third-largest school district, is "not primarily motivated by money... but [instead] whether teachers should be held accountable for failing public schools," according to the LA Times. Chicago Mayor Rahm Emanuel has offered teachers a 16% pay raise over four years and other new benefits that the teachers' union has supported in negotiations.

The walkout is the largest private- or public-sector strike in the United States since 29,000 California nurses and medical workers staged a walkout in Sep. 2011. 

Chicago Teachers Union (CTU) President Karen Lewis said in a statement, "[our] concern is evaluation procedures. After the initial phase-in of the new evaluation system it could result in 6,000 teachers (or nearly 30 percent of our members) being discharged within one or two years. This is unacceptable. We are also concerned that too much of the new evaluations will be based on students’ standardized test scores. This is no way to measure the effectiveness of an educator. 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."

Under Illinois' "Performance Evaluation Reform Act of 2010" bill, passed as part of the federal "Race to the Top" education initiative, public schools must incorporate standardized tests as a "significant factor" in their evaluations of teachers. The Illinois state school board defined "significant factor" to mean 20-40 percent of those evaluations' content. The bill is in the process of implementation, but is expected to "give standardized tests a larger role than they have relative to, say, seniority or education level when determining, for example which teachers get laid off during budget crunches," according to the Washington Post.

Republican Presidential candidate Mitt Romney released a statement saying, "I am disappointed by the decision of the Chicago Teachers Union to turn its back on not only a city negotiating in good faith but also the hundreds of thousands of children relying on the city’s public schools to provide them a safe place to receive a strong education. Teachers unions have too often made plain that their interests conflict with those of our children..."

According to the Pew Center on the States, annual state spending on standardized tests rose from $423 million before No Child Left Behind to almost $1.1 billion in 2008. Combined state and federal government spending on education totals $600 billion per year, while all-time philanthropic contributions to US education total less than $10 billion, according to a 2011 statement by education philanthropist Bill Gates.