Thousands of Denver public school teachers walked picket lines for a second day on Tuesday, disrupting classes for some 92,000 students as union and school district officials resumed contract talks that broke down over the weekend.

In the latest in a series of strikes to hit U.S. public school systems around the country, the 5,650-member Denver Classroom Teachers Association is seeking higher pay with a salary structure focused less on performance bonuses and more on cost-of-living increases.

The Denver labor dispute follows statewide teacher walkouts last year in West Virginia, Kentucky, Oklahoma and Arizona, and a six-day strike in Los Angeles settled last month with a deal to reduce class sizes and raise salaries by 6 percent.

Talks in Denver broke down on Saturday, triggering the first walkout by teachers in Colorado’s largest city since 1994. The two sides returned to the bargaining table late on Tuesday morning.

Outside Columbian Elementary school, a dozen teachers picketed, including early childhood education specialist Traci McKeehan, 48, who said she was hopeful a deal would be reached with a more predictable pay structure. The union says the current system has led to wide individual wage fluctuations from year to year, leading to higher rates of teacher turnover.

“In Denver, we’re losing teachers left and right,” said McKeehan, who was holding a sign that read, “We’d rather be teaching.”

The Denver Public Schools district has said its latest proposal would raise teachers’ pay by nearly 11 percent next year, while the union has called that figure inflated.

On Monday, Public Schools Superintendent Susana Cordova told reporters that the district has already met many of the teachers’ demands for simplifying their complicated pay structure.

“We’ve made really significant changes already,” Cordova said. “Many of the things I think that we hear our teachers complain about, actually aren’t about the proposal that we’ve put on the table, it’s about the current system. And many of those things I agree with as well.”

District officials vowed to keep all 207 schools open through the strike, staffed by substitute teachers and administration personnel. But on Tuesday the district said it canceled pre-kindergarten classes.

The so-called ProComp pay system at the crux of the strike was initially embraced by the union when it was instituted in 2005, touted as a way of enabling teachers to build their salaries through a mix of possible incentives. Those include bonuses tied to student achievement and tougher teaching assignments, such as schools in high-poverty areas.

But the union says ProComp, one of the longest-running teacher pay schemes of its kind in the country, has instead eroded teacher pay in a city where the cost of living has soared in the past 10 years.

Denver Mayor Michael Hancock on Monday expressed support for the teachers’ pay demands and offered to help mediate the dispute.

Reporting by Keith Coffman in Denver; Additional reporting by Jann Tracey in Denver and Gina Cherelus in New York; Writing and additional reporting by Peter Szekely in New York, Rich McKay in Atlanta and Steve Gorman in Los Angeles; Editing by John Stonestreet and Matthew Lewis