CHICAGO (AP) — For the first time in a quarter century, Chicago teachers walked out of the classroom Monday, taking a bitter contract dispute over evaluations and job security to the streets of the nation’s third-largest city — and to a national audience — less than a week after most schools opened for fall.

The walkout forced hundreds of thousands of parents to scramble for a place to send idle children and created an unwelcome political distraction for Mayor Rahm Emanuel. In a year when labor unions have been losing ground nationwide, the implications were sure to extend far beyond Chicago, particularly for districts engaged in similar debates.