The Service Employees International Union, Local 99, represents 33,000 of the lowest-paid employees in the nation's second-largest district, including custodians, teaching assistants, security aides and cafeteria workers. Some made $8 an hour last year.
The union hailed both the local and broader impact.
"This historic agreement sets a new standard for ending poverty in our schools," said Local 99 Executive Director Courtni Pugh. "This will be felt in school districts across Los Angeles and across the country."
With Washington, D.C., stalled in legislative gridlock, the "Fight for 15" campaign, as it is known, has achieved particular resonance in more liberal, diverse cities, where the cost of living frequently is higher.
Seattle has approved a gradual move to a $15-per-hour minimum. San Francisco has put the idea on the November ballot. A group of employers at Los Angeles International Airport has signed on, and city officials are drafting an ordinance that would require larger hotels to pay at least $15.37 an hour.
Such efforts often are spearheaded by locals of Service Employees International.
"This is a giant first step in making sure that school jobs are good jobs," Pugh said. "Mom and Dad can help with their children's homework instead of clocking in for their second job."
Some observers struck a cautionary note.
"Funds that are now going to be redirected to low-wage workers will have to come from somewhere," said Lance Izumi, senior director of education studies at the Pacific Research Institute, a conservative think tank based in San Francisco. "Where will that belt-tightening occur? How much effect will that belt-tightening have on children in the classroom?"
He added: "While revenues are better now, it was just a couple years ago that LAUSD ran deficits in the hundreds of millions of dollars. With California's economy subject to roller coaster ups and downs, is it prudent to nearly double the wages of these employees?"
The school board approved the pact unanimously. L.A. Unified has benefited from an improving economy and state policy that provides increasing funding to schools with low-income students.
L.A. schools Supt. John Deasy strongly endorsed the $15 minimum, calling it "philosophically easy" if "financially difficult."
Through education, "we lift youth out of poverty every single day," he said. The school system must do its part, he added, "to make sure parents are not remaining in poverty."
Board members were unreservedly enthusiastic.
"As our nation struggles with questions about justice and fairness for low-wage workers, LAUSD must lead by example," said one, Steve Zimmer.
Tamar Galatzan praised the contributions of the workers: "You keep our schools clean, you make sure our kids get to their field trips safely and on time, you wipe runny noses, you ensure the transcripts and paperwork go out — you lead our school communities."
The new contract is a testament to the clout of both the union's campaign dollars and the ground troops it can assemble for an electoral campaign.
Local 99 has scored notable victories in recent years. In 2007, part-time cafeteria workers received health benefits for themselves and their families. Later, jobs and working hours increased for food workers when the district began requiring breakfast for students in their classrooms.
And the district responded to the 2012 Sandy Hook school shooting in Connecticut by hiring hundreds of unarmed security aides — all union members.