Denver’s public school teachers went on strike Monday, following the lead of teachers across the country who have refused to go to work until they get a raise.

The walkout comes after more than 15 months of tense negotiations between the school district and the teachers union over the compensation system, which relies heavily on bonuses that fluctuate wildly from year to year.

Teachers say their salaries are too low for Denver’s high cost of living and aren’t keeping up with pay in neighboring districts. They also point out that the district has way more administrators than other districts of similar size, which eats into the school budget.

Denver officials said they are listening, and that they’re willing to give teachers a raise but want to keep offering bonuses to teachers who work in high-poverty communities.

“We’re disappointed that the [Denver Classroom Teachers Association] walked away from the table. We presented an updated proposal that responds to what we have heard from teachers, aligns to our values of equity and retention, honors the ProComp ballot language and significantly increases the base pay for teachers,” the district stated on Monday, after negotiations fell apart over the weekend.

City and state officials tried hard to keep teachers from going on strike. Colorado lawmakers threatened them with jail time. School administrators asked the governor to stop them. Neither effort worked, though, and more than 2,000 teachers are now picketing on the streets.

“Now is our time,” Sonia Burns, a Denver high school social studies teacher, told me. “There is a movement around the country and we’ve gotten so much support from the community.”

Unlike other districts where teachers went on strike, Denver officials have decided to keep the schools open during the stoppage, counting on administrators and substitute teachers to keep students on schedule. However, preschool classes were canceled Monday because they couldn’t find enough licensed teachers to fill in.

Burns, who has been teaching in Denver for eight years, said teachers are nervous but determined. The school district has offered educators a 10 percent raise, but the Denver Classroom Teachers Association, a labor union representing about 5,700 educators, wants the district to overhaul the entire compensation system.

Arbitrary bonuses and low pay

Teachers are most upset about Denver’s incentive pay system, which started more than a decade ago. The district pays bonuses based on teacher performance, and to encourage teachers to work in high-poverty schools.

But the union says the bonuses vary too much from year to year, creating financial instability for educators and their families. They also say it’s unclear how the district measures good performance and determines bonuses.

Instead, teachers want the district to lower bonuses and increase their base salaries, and to give them salaries based on education and training, like most school districts do.

Colorado teachers are among the lowest-paid in the country, earning an average of $46,155 in 2016 — ranking Colorado 46th in average teacher pay, according to the National Education Association. The state also spends about $2,500 less per student each year than the national average.

The Denver Classroom Teachers Association voted to authorize a strike in January with support from 93 percent of its members. At the time, the two sides were about $8 million apart in reaching an agreement.

After authorizing a strike, the school district fought back. They asked Gov. Jared Polis to intervene, a legal move that delayed the strike as the state government weighed its options. But last week, the governor declined to intervene in the dispute, which could have further delayed a strike by up to 180 days.

That wasn’t the first attempt to keep teachers from going on strike, though. Far from it.

Republican lawmakers tried to make striking illegal

In April, two Republican state legislators tried to shut down a potential teachers strike in Colorado with the threat of jail time.

The bill, introduced in the state Senate, prohibited districts from supporting a teachers strike and required schools to dock a teacher’s pay for each day they participate in a walkout. The teachers could also have faced up to six months in jail and a $500 daily fine if they violated a court order to stop striking.

The bill was a reaction to the teacher strikes sweeping red and purple states, including Oklahoma, West Virginia, Arizona, and Kentucky. Thousands of teachers in Colorado had joined the grassroots movement, holding rallies at the state capitol to demand a pay raise and more funding.

The bill failed. And now the teachers are on strike in Denver — for the first time in 25 years.