"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, President Barack Obama's former chief of staff.
The school district asked community organizations to provide additional programs for students, and a number of churches, libraries and other groups plan 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 teachers' protests as well as the thousands of students who could be roaming the streets.
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."
Emanuel and the union officials have much at stake. Unions and collective bargaining by public employees have recently come under criticism in many parts of the country, and all sides are closely monitoring who might emerge with the upper hand in the Chicago dispute.
The timing also may be inopportune for Emanuel, whose city administration is wrestling with a spike in murders and shootings in some city neighborhoods and who just agreed to take a larger role in fundraising for Obama's re-election campaign.
As the strike deadline approached, parents spent Sunday worrying about how much their children's education might suffer and where their kids will go while they're at work.
"They're going to lose learning time," said Beatriz Fierro, whose daughter is in the fifth grade on the city's Southwest Side. "And if the whole afternoon they're going to be free, it's bad. Of course you're worried."