CHICAGO, IL - SEPTEMBER 11: Chicago public school teachers and their supporters picket in front of the Chicago Public Schools (CPS) headquarters on September 11, 2012 in Chicago, Illinois. More than 26,000 teachers and support staff walked off their jobs yesterday after the Chicago Teachers Union failed to reach an agreement with the city on compensation, benefits and job security. With about 350,000 students, the Chicago school district is the third largest in the United States. (Photo by Scott Olson/Getty Images)

CHICAGO, IL - SEPTEMBER 11:  Chicago public school teachers and their supporters picket in front of the Chicago Public Schools (CPS) headquarters on September 11, 2012 in Chicago, Illinois. More than 26,000 teachers and support staff walked off their jobs yesterday after the Chicago Teachers Union failed to reach an agreement with the city on compensation, benefits and job security. With about 350,000 students, the Chicago school district is the third largest in the United States.  (Photo by Scott Olson/Getty Images)