The Chicago Teachers Union strike is in full swing as thousands of the city’s teachers showed up to their respective schools this morning not to work, but to strike for the first time in 25 years.

While issues such as health benefits, teacher evaluations, and job security are still key elements to the ongoing contract negotiations between the union and the city, some teachers said that’s not the whole story.

“We’re talking not just about the raises. We’re talking about having an extended school day and longer school hours, losing our arts and our music and our enrichment programs, having not nearly enough social workers in the school, nor nurses, to take care of the needs of our students,” said Katie Lira-Luna, literacy instructional coach at Roberto Clemente High School.

Lira-Luna was joined by about three dozen CTU members and supporters who received numerous honks and waves of support from passing motorists along Western Avenue this morning.

Some of those supporters shouted in agreement with Lira-Luna as she stressed that the strike is not only about salaries and tenure, but also about providing a quality education and up-to-date facilities, complete with working air-conditioners, for Chicago’s public schoolchildren.

Mayor Rahm Emanuel, however, disagreed completely with that argument.

"Everything here is down to two final issues. It's not air conditioning, OK. It's 71 degrees outside, it's not air conditioning. We don't go on strike for air conditioning. Two issues, fundamental: an evaluation system designed by teachers, for teachers, revised by teachers. A system in which the local principal picks the most qualified teacher to teach or downtown does it. And I'm against downtown. I want the local school principal, your neighborhood school principal, picking the best qualified teacher,” Emanuel said at press conference early Monday afternoon.

The newly proposed teacher evaluation system has become a major talking point for CTU Vice President Jesse Sharkey. He told WGN-TV this morning that the new system would tie teacher evaluations too closely to standardized testing, a decision that could make about 6,000 teachers eligible for dismissal by next year.

Teachers said there are too many variables in the classroom to be effectively measured by standardized testing, such as childrens' individual learning styles.

A back-up plan has been implemented by CPS where 144 school sites will remain open during the strike from 8:30 a.m. until 12:30 p.m. Students will not receive formal classroom teaching, but they will have access to breakfast, lunch and daily activities and supervision. Chicago police are also stepping up patrols in areas of the city that are expected to see an increase in the number of children playing outside.

All of Chicago’s charter schools will maintain a normal school schedule during the strike.

Chicago Public Schools is the nation’s third largest public school system serving about 400,000 students and is made up of about 20,000 teachers.

Here's a look at the scene at Clemente high school this morning:

Check back with Progress Illinois later today for our ongoing coverage of the Chicago teachers' strike.