CHICAGO — Democratic presidential candidate Elizabeth Warren called for people across the country to support striking Chicago teachers after joining educators picketing outside an elementary school on Tuesday, the fourth-day classes have been canceled in the nation’s third-largest school district.

The Massachusetts senator took photos with teachers gathered outside the West Side elementary school and told the crowd that her experience in a New Jersey teaching job makes her appreciate their work and support the strike.

“I’m here because the eyes of this nation are upon you,” Warren said. “They have turned to Chicago, for you to lead the way, for you to show how the power of standing together is the power of making real change in this country.”

The Chicago Teachers Union’s 25,000 members and Chicago Public Schools remain at odds over teacher pay, limits on class sizes and additional support staff in schools. Thousands of support staff also are on strike alongside teachers.

Negotiators reported some progress over the weekend but on Monday night union leaders said talks had stalled and blamed Mayor Lori Lightfoot.

Earlier Monday, Lightfoot sent a letter to union leaders asking for teachers to return to work without a deal as contract talks continued and reiterated her concern that teachers’ demands are unaffordable for the district.

CTU President Jesse Sharkey described Monday’s talks as “taking a turn for the worst,” and said city and district negotiators were following the mayor’s lead.

“She wants us to simply give up on some of the most basic things that we’re asking for and that’s not the way that labor negotiations work,” he said on Tuesday morning.

Lightfoot defended her approach and said she will continue talking about hardships that the strike causes for families, including student-athletes who are prevented from practicing or competing during a walkout and high school students trying to meet college application deadlines.

“What we’re seeing is real, human cost for this work stoppage,” Lightfoot said.

She added that the district’s finances still are shaky and heavily dependent on borrowing. The district has estimated all of teachers’ demands would add $2.5 billion to the district annual budget and officials call that unaffordable.

“This idea that we’re flush with cash and just sitting on it and not spending it on the things that we both agree matter just isn’t true,” said Janice Jackson, the district’s chief executive officer.

Lightfoot, a Democrat who was elected on a progressive platform, said she expects all members of her party “to support workers” but dismissed a suggestion that visits like Warren’s could shape contract talks.

“People are going to come in to catch a moment and then they’re going to leave,” she said. “What’s most important is that the people of Chicago know about what’s going on.”