CHICAGO (AP) — MN For the first time in a quarter-century, thousands of Chicago teachers walked off the job Monday, escalating a bitter contract dispute over evaluations and job security and forcing parents to scramble for somewhere to send idle children.

Both sides went back to the bargaining table around midday, hours after the walkout began when the two sides failed to agree on a contract before a midnight deadline. The strike affected nearly 400,000 public school students and their families in the nation’s third-largest district.

While negotiators said they had made progress on salary and a longer school day, they remained divided on a host of other issues.

Chicago Mayor Rahm Emanuel pushed to end the confrontation quickly. He repeatedly said negotiators were within reach of a deal and that the strike was unnecessary. The mayor acknowledged tensions with union over longstanding issues, but urged a quick resolution.

“Don’t take it out on the kids of Chicago if you have a problem with me,” Emanuel said Monday at one of the churches that is serving as a gathering spot for students during the strike.

Some 26,000 teachers and support staff were expected to join the picket line, and events were planned all day long. At Paul Robeson High School on the city’s South Side, two dozen teachers wearing red shirts chanted and carried signs saying “On Strike For Better Schools.”

“There’s been a large disinvestment in neighborhood public schools,” said Jeremy Peters, who’s taught civics and U.S. history for a decade. “It’s an absolute debacle.”

To give students a place to go, district officials said some 140 schools would be open for the first half of the day so children who rely on school-provided free meals can eat breakfast and lunch. More than 80 percent of district students qualify for free and reduced-price lunches.

City officials acknowledged that children left unsupervised — especially in neighborhoods with a history of gang violence — might be at risk, but Emanuel vowed to protect students.

“We will make sure our kids are safe. We will see our way through these issues, and our kids will be back in the classroom where they belong,” said Emanuel, the former chief of staff to President Barack Obama.

The school district asked community organizations to provide additional programs for students, and a number of churches, libraries and other groups planned to offer day camps and other activities.

Police Chief Garry McCarthy said he would take officers off desk duty and deploy them to deal with any protests as well as the thousands of students who could be roaming the streets. Chicago police reported no problems or violence related to the strike.

Union leaders and district officials were not far apart in their negotiations on compensation, Chicago Teachers Union President Karen Lewis said. But other issues — including potential changes to health benefits and a new teacher evaluation system based partly on students’ standardized test scores — remained unresolved, she said.

“This is a difficult decision and one we hoped we could have avoided,” Lewis said. “We must do things differently in this city if we are to provide our students with the education they so rightfully deserve.”

Republican presidential nominee Mitt Romney said Chicago teachers were turning their backs on thousands of students and that President Barack Obama was rooting for the striking educators.

Obama’s top spokesman said the president has not taken sides but is urging both the teachers and the city to settle quickly.