Children joined striking Los Angeles teachers walking the picket line Monday at Baldwin Hills Elementary School. It was the first teachers strike in 30 years. (David McNew/For The Washington Post)

LOS ANGELES — Teachers in the nation’s second-largest school system walked off the job Monday, heading for rain-soaked streets amid a battle with district leaders over crowded classrooms, depleted staff and the very future of Los Angeles schools.

The strike drew thousands of unionized teachers to the picket lines, where they marched in front of schools in unrelenting rain, wearing red ponchos and rain boots. The walkout affected more than 30,000 educators and 600,000 schoolchildren across the sprawling district, which encompasses 710 square miles and hundreds of K-12 schools, making it larger than many state systems.

The job action, the first teachers strike in Los Angeles in three decades, follows a year in which educators in a half-dozen GOP-controlled states walked out to demand raises and more money for schools. But this movement, taking place in the heart of deep-blue California, is no red state revolt.

Instead, it highlights an existential fight unfolding in urban school systems across the nation and in the Democratic Party: Should public classrooms be surrendered to private operators, taking students and dollars from traditional schools?

In Los Angeles, that fight is especially evident. In some schools, the traditional public system occupies one wing while another corner of the school houses a charter operator.

And the actors in the battle here are quintessentially L.A.: tech and film giants, and philanthropists with big wallets and connections to the arts and high society.

“Schools are not playgrounds for the rich. They belong to the people of Los Angeles,” said Alex Caputo-Pearl, president of United Teachers Los Angeles, the union representing educators.

The union is demanding that the school system invest in reducing class sizes and hiring more support staff. Many schools have nurses only one day a week, and counselors are overburdened with students. The union, which also seeks a 6.5 percent pay raise, hopes those investments will prevent families from leaving comprehensive public schools for the city’s robust charter school network, taking state funding with them. Average class size hovers above 32 students for middle and high school students, with some teachers contending with up to 42 students in a single class.

About 90 percent of the district’s funding comes from the state, which in 2016 ranked 41st in the nation in per-pupil spending funding when the cost of living was taken into account.

Maria Arienza, who teaches AP Spanish at North Hollywood High, said she had 49 students in a single class last semester.

“My kids don’t have enough desks,” said Arienza, who has taught for seven years. “They sit on the floor in a crowded classroom.”

Outside Baldwin Hills Elementary on bustling Rodeo Road, teacher Marie Germaine said the district has given a charter school space on their campus. It means the predominantly African American school, with a premier gifted program, no longer has a computer lab or art room. An occupational therapist now meets with students in a storage closet.

“We have a charter school on campus that is eating away at our spaces, our resources,” Germaine said.

But schools superintendent Austin Beutner, a former investment banker and nonprofit executive who was hired to get the system’s finances in order, said the district cannot afford the union’s demands. The school system presented another offer to the union last week, after the newly installed governor, Gavin Newsom (D), pledged to give Los Angeles schools more money. But it was not close enough to the union’s demands.

“If we agreed to UTLA’s demands, the district would become immediately bankrupt and would be taken over by the state that same day,” Beutner said in an interview Saturday. “That’s the fact.”

Beutner disputes the notion that he favors charter schools — which are privately run but publicly funded — over traditional public schools, saying that charter school policy is made at the state level.

“I’m not a charter guy. I’m not a no-charter guy,” Beutner said in the interview. “I don’t think charters are the solution. I don’t think they’re the problem, either. I believe in choice.”

The school system remained open, deploying central office staff to classrooms across the city and bringing in high-priced substitutes to teach and supervise children. About 1 million meals are served every school day, with three-quarters of schoolchildren qualifying for free meals because they come from low-income households.

Many parents are keeping their children out of school, because of safety concerns or in solidarity with teachers.

Some of the striking teachers are being joined by students, who said they have felt the effects of the system not investing sufficiently in their education.

Makailah Jenkins, 16, is a junior at Washington Preparatory High in South Los Angeles. One of her classes was so crowded that she had to stand until a student transferred, freeing up a seat. There is no one to teach AP U.S. History, so she takes it online.

“I am being affected by these things as well,” Jenkins said. “It’s my duty to make my voice heard.”

Max Jimenez, an 18-year-old senior at James Monroe High in the North Hills section of Los Angeles, joined throngs of protesters at a rally Monday, coming with several classmates. Making his first-ever appearance at a protest, he said he was taking a lesson from his AP government teacher — about the importance of standing up for his beliefs — to heart.

“I’ve only seen this . . . in movies,” Jimenez said, marveling at the crowd.

The strike is the continuation of a long-running battle in the state between Democrats who align themselves with unions, and those who back charter operators.

The latter group includes wealthy philanthropists such as Eli Broad, whose namesake contemporary art museum sits on a hill above downtown Los Angeles; Reed Hastings, chief executive of Netflix; and former New York mayor Michael Bloomberg. The three men donated millions of dollars in a bid to elect former Los Angeles mayor Antonio Villaraigosa to the governor’s office. He was trounced in the primary by Newsom. Teachers unions backed Newsom.

Charter backers also spent tens of millions of dollars in a bid to elect a former charter network CEO as state superintendent of public instruction, a role that has little power over charter school policy. He was edged out by Tony Thurmond, who was backed by teachers unions in the most expensive state school chiefs race in history, with campaign contributions topping $40 million.

The clash in Los Angeles is viewed by some as the latest chapter in the long-running — and expensive — battle for the future of California schools.

At a news conference Monday morning, Beutner urged the union to come back to the bargaining table and said he had engaged Newsom, Mayor Eric Garcetti (D) and Thurmond.

“It is our desire to have our educators well-supported and back in our schools serving the needs of our students,” Beutner said.

“We shouldn’t be putting kids in the middle of this existential conversation about public education,” the superintendent said Saturday.

Asked how long the strike would last, Caputo-Pearl said Sunday evening that teachers “are prepared to strike for as long as it takes.”

Debbie Truong in Washington contributed to this report.

correction: An earlier version of this report erroneously stated the winner of the race for California superintendent of public instruction. Tony Thurmond was elected to the role.