Transcript for Chicago Teachers' Strike: Public Schools vs. Charter Schools
Now to the big showdown in chicago. 29,000 teachers still on strike. 350,000 schoolchildren on pause. Tonight, the battle is being watched from hawaii to maine, at least 23 states debating the same question. How do you grade a teacher? Abc's alex perez in chicago. Reporter: Union teachers holding strong at the picket line in chicago, refusing to back down. We did not start this fight! Reporter: The fight is about a program that would eventually base as much as 40% of a teacher's evaluation on standardized test scores. A formula the union argues will unfairly cost teachers their jobs. Mayor rahm emanuel believes the new measure will help turn around the districts' staggering statistics. It's about ensuring that over a period of time we have a way to raise the quality of the teachers. Reporter: The numbers are sobering. Thattistic, for every 100 chicago public school freshmen, only 8% get four year college degrees. While the strike continues it's been business as usual for 52,000 other chicago public schoolchildren. They attend charter schools like uno school on chicago's southwest side. Public schools tied to nonprofit organizations who create their own achievement goals and routinely out-perform noncharter public schools. Why do you feel that charter schools are better than your average public schools? I feel that charter schools create an environment of competition. Reporter: Cash competition. Teachers at uno can earn an $8,000 bonus if their students perform well. And they do. Last year 100%, that's 107 students, went on to college. Here more of the teacher's evaluation is based on standardized tests, 50%, and teachers don't belong to a union. What's the biggest difference between you and a union teacher? We aren't protected as far as our jobs if we don't perform. Reporter: So which model works? That's the question at the heart of the largest teachers strike in two deck kasd with no immediate end in sight. Alex perez, abc news, chicago.
This transcript has been automatically generated and may not be 100% accurate.