(CNN) More than 37,000 children are out of school after the St. Paul, Minnesota, teachers union went on strike because a dozen mediation sessions had not yielded meaningful movement on educators' demands for better mental health and multilingual services for students.

The language support is especially important in one of the nation's most diverse districts, where families speak 129 different tongues, the St. Paul Federation of Educators says.

As for the mental health support staff, many students are experiencing trauma, the union says. In a 2019 survey, almost one-fifth of eighth-grade girls said they'd considered suicide in the last year, and 40% of fifth-graders agreed with the statement, "I worry a lot."

Teachers are also asking for an expansion of "restorative practices to start eliminating the racial disparities in our schools," a union statement said

About one-third of St. Paul students are learning English, about 15% require special education and roughly seven in 10 are eligible for free or reduced lunches, according to district statistics

Calling the strike avoidable and unnecessary, St. Paul Public Schools Superintendent Joe Gothard said his team did everything it could to appease teachers. That included offering wage increases totaling almost $10 million and filling some of the union's requested 300 new positions -- but it wasn't enough, he said.

"I want to make it clear: I believe our students need and deserve additional support," Gothard said. "However, we must prioritize our spending because we have limited resources. We need to place new investments where they are needed most."

After reviewing the district's final offer, the union announced its first strike in 74 years at about 3 a.m. Tuesday and instructed educators to report to the picket line or contact their strike captain for other ways to participate.

"What we're asking for is about 4% of the district's total budget, right? So this is not a budget issue," union president Nick Faber said at a news conference.

No 'secret pot of money'

Gothard this week requested arbitration as a means of keeping the schools open, but the union rejected the proposal, the Star Tribune in Minneapolis reported

The school board felt the union's proposals would endanger funding and resources for other unions and force cuts to other programs when the district's limited resources require school officials to be "intentional and responsible when increasing investments," board chairwoman Marny Xiong said in a statement . District employees are represented by 27 unions, according to the school system

The points of contention are about priorities not money, Faber says, but the district disagrees.

"The reality is that there isn't a secret pot of money hiding somewhere," Xiong told the Star Tribune.

Asked whether teachers were hoping Minnesota lawmakers might step into the fray, Faber told reporters he had no expectations to that effect.

"This is a priorities issues, and sure, it would be great for the state to step up, but we've been waiting for the Legislature for a long time ... and currently all we're getting is a constitutional amendment that's not going to get us where we need to go," he said.

Legislators are considering an amendment that opponents say would tilt the playing field to the detriment of poorer students and open the door to "taxpayer-funded vouchers for private schools," according to Education Minnesota , which does not support the amendment.

'It's emotional'

Cassie Heeringa has taught at Crossroads Elementary for five years. On Tuesday, a yellow sign out front declared, "No school today."

She stepped away from a pack of protesters -- many clad in "red for ed" and carrying picket signs that said, "A strike for the schools St. Paul children deserve" -- to talk to CNN affiliate WCCO about the importance of her children feeling secure and being able to concentrate. Teachers spend too much time working to correct "difficult behaviors" when they should be focused on educating, she said.

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"It's emotional. Yesterday, putting the kids on the bus, I was crying on the inside because I love my students, and this is for them. We want them to feel safe. We want them to learn. They deserve more," she told the station. "All of us our giving up our incomes, our insurance. I have a child at home. I know a lot of these people have more than one child and we're giving up a lot, but we know that it's the right thing to do for our students and for each other."

Faber echoed Heeringa's assertion that teachers take no joy in classes being canceled.

"Educators want to be with their students, but they also want their students to enter schools that are supported and have the resources our kids need to thrive," he said. "Students being out is not where we want to be. Our educators don't want to be out as well, but I think at certain times we've got to to step up and make these sacrifices so that our students get what they need."

Months of negotiations

Though Faber reported "some movement" during overnight negotiations, it was not sufficient to stave off a strike, he said. "We were nowhere close to where we needed to be," he said, adding that educators are happy to return to the table if the district comes up with any new offers.

The union is instructing teachers to report to strike lines from 7 a.m. to 11 a.m. -- and participate in a "district-wide action" from 1 p.m. to 3 p.m. -- every day until an agreement is reached.

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Educators who cross the picket line will not lose their membership or face legal action, but they will not be eligible for interest-free loans from the union strike fund and the union's executive board will recommend that strikebreakers no longer be eligible for part-time employment within the union, the union's bargaining team informed teachers in a letter

"The picket line is where we show our strength to the district, and it's where we get to stand together and fight," the letter said. "When people cross the picket line, it weakens our bargaining position and can potentially make a strike drag out even longer."

With the help of non-striking employees, beginning Thursday, the school system will provide supervised activities to students in kindergarten through fifth grade. It will also provide all students free breakfast and lunch at designated sites, beginning immediately, the district said.