LOS ANGELES (AP) — A three-day strike by workers in the Los Angeles Unified School District ended Thursday, but it wasn’t immediately clear if any progress was made in negotiations for higher pay for teachers’ aides, bus drivers, custodians and other support staff in the nation’s second-largest school system.

Teachers joined the picket lines in solidarity, shutting down instruction for the district’s half-million students during the walkout by members of Local 99 of the Service Employees International Union, which represents about 30,000 of the lowest-paid school workers. Support staffers earn, on average, about $25,000 a year in Los Angeles, barely enough to get by in one of the most expensive cities in America.

Mayor Karen Bass stepped in as mediator Wednesday after district Superintendent Alberto M. Carvalho accused the union of refusing to negotiate.

Max Arias, executive director of SEIU Local 99, said the union was grateful that Bass was helping “find a path out of our current impasse.” There was no indication Thursday how the arbitration was going.

“Education workers have always been eager to negotiate as long as we are treated with respect and bargained with fairly, and with the mayor’s leadership we believe that is possible,” Arias said.

Carvalho has called the school district’s offer “historic.” It includes a cumulative 23% raise, starting with 2% retroactive as of the 2020-21 school year and ending with 5% in 2024-25. The package would also give a one-time 3% bonus to those who have been on the job more than a year. It would also add more full-time positions and expand health care benefits.

Sofia Munoz, a special education teacher’s assistant, said she hoped the labor action sent a message to Carvalho.

“We’re hoping just to bring awareness and let the superintendent know that we’re here to make a difference,” Munoz said Thursday at a rally marking the strike’s final day.

The school district confirmed in a statement Wednesday that school officials have been in talks with union leaders with help from the mayor.

“We continue to do everything possible to reach an agreement that honors the hard work of our employees, corrects historical inequities, maintains the financial stability of the district and brings students back to the classroom,” the statement said.

The union said employees, including special education assistants, cafeteria workers and gardeners, would return to work Friday.

The strike concluded after putting a spotlight on the issue of notoriously underpaid workers who serve as the backbone of schools across the country.

SEIU Local 99 says many of its members live in poverty because of low pay or limited work hours while struggling with inflation and the high cost of housing. The union is seeking a 30% raise for workers.

While the Los Angeles Unified School District is unique because of its size, the walkout could have lessons for other systems in the state, said Troy Flint, spokesperson for the California School Board Association.

“LAUSD could be the canary in the coalmine when you look at the potential for difficult labor negotiations in school districts across California,” he said.

Districts are coping with staff shortages and other challenges exacerbated by the COVID-19 pandemic, while working to address other longstanding issues including student performance that predated the pandemic, according to Flint. In addition, emergency pandemic funding from the state was set to expire next year, which will stretch district finances even thinner after decades of underfunding, he said.

“It’s natural that employees want to better compensated for their important work,” Flint said. “There is a lot of tension between what districts want to do and what they have the capacity to do.”

Leaders of United Teachers of Los Angeles, which represents 35,000 educators, counselors and other staff, pledged solidarity with the strikers.

Experts say it is unusual for different unions in the same school district to band together but the unified labor action in Los Angeles could mark an inflection point.

Luz Varela, a teacher’s aide, said workers felt like they had to strike.

“I feel sad that we have to go through this because we’re missing our kids, but we’re doing this for our kids,” she said. “I feel that we deserve a little bit more. It’s not all about the money. This is about our future for our kids.”