(CNN) - An army of Denver teachers braved freezing temperatures Monday, sacrificing pay to strike for a better future.
But even though this strike focuses on teachers' salaries, students joined them on the picket lines, saying their teachers deserve better.
"It's like they make school fun. They make you want to be there," 16-year-old Xavion Davison said.
He and friends Allen Koncsik and Bryce Alexander carried a large sign proclaiming, "They deserve more than just praise. Give them a raise."
Denver teachers say they want higher, stable salaries, since their school district uses unpredictable bonuses to compensate for low base pay.
"Unfortunately bonuses are really variable, and we can't depend on them from year to year," social studies teacher Nick Childers said.
Ninth-year teacher Kelsey Brown said the bonuses are so erratic, she made more money two years ago than she does now.
The Spanish teacher made $56,000 last year, but the rising cost of living in Denver means she has to work extra jobs -- as a lacrosse coach, exchange program coordinator and summer camp employee.
Now, after 15 months of failed negotiations between the school district and teachers' union, educators are ditching classrooms to march up and down snow-lined sidewalks.
The Denver Classroom Teachers Association, which represents most of Denver's 5,000-plus teachers, said it doesn't want to strike -- but said the school district hasn't met their demands.
"We're hoping for a quick solution to this whole thing," DCTA lead negotiator Rob Gould said Monday. "We're hoping (school district officials) come to the table tomorrow ready to listen so we can get back to work. Because our teachers want to be in the classrooms with their kids."
Denver Public Schools said it's listened to teachers' concerns and made a series of offers to the union -- all of which have been rejected.
"I am extremely disappointed that the DCTA walked away from the table," Superintendent Susana Cordova said after talks broke down Saturday night. "We presented an updated proposal that responds to what we heard from our teachers ... and significantly increases the base pay for all of our educators."
She said both sides will be back at the negotiating table Tuesday.
"It's a problem for our kids not to have their teachers in class," she said. "So I want to get this done now."
What both sides have put up
Denver Public Schools says it's offered:
-- $23 million in new funds next year for teachers' base salaries. (That would increase the average teacher's salary from about $55,000 to $61,000 next year.)
-- A total investment of $55 million over the next three years.
-- An increased starting salary of $45,800 for new teachers.
-- Another $2 million investment in base pay for teachers and specialized staff members that would "come from additional, painful cuts to our central departments, which we estimate to be an elimination of about 150 positions in the central office."
-- The elimination of performance bonuses for central office senior staff. "We would invest those funds directly in our highest-needs schools, with a proposed increase in incentive pay for teaching in our schools with the highest poverty rates," the school district said. "Our offer increases that incentive from $2,500 to $3,000."
DPS illustrated how its concessions to the union -- more than $20 million since last June -- is significantly more than the union's decrease in demands.
But the union said it's still waiting for "a fair, competitive and transparent salary schedule that prioritizes base salary over complicated, unreliable bonuses."
"We are incredibly disappointed that on the last day of bargaining and less than two days before a strike, they doubled down on one-time incentives teachers do not want, and the data shows do not work to keep teachers in their schools," DCTA President and teacher Henry Roman said.
What students will do without their teachers
Despite the strike, DPS encouraged students to go to school this week. All schools except preschools are still running on normal schedules.
But 2,631 teachers did not go to school Monday, DPS spokeswoman Anna Alejo said. That's about 56% of teachers from district-run schools.
In other words, about half of DPS' 92,000 students have no idea when they'll see their teachers back in class again.
To make up for those 2,631 missing teachers, about 1,400 central office staffers and 400 substitute teachers covered teacher absences Monday, Alejo said.
But Xavion said substitutes can't teach like his normal teachers.
"I don't feel like I'm learning anything. It's not the same," the teen said. "With our teachers, I feel like we're in a better learning environment. Not with any sub."
Some teachers are too broke to strike
Since teachers aren't getting paid while on strike, not every teacher who wants to strike can do so.
"I really, really want to because I do support the mission ... but I literally financially cannot afford to," said math teacher Sophia Leung. "For me to lose out on $200 of pay a day, it does impact my bills for the month."
And as a first-year teacher, Leung said she can't even afford the $70 monthly dues to join the local teachers' union.
But this renewed wave of teachers' strikes shows the sacrifices teachers are willing to make, said Randi Weingarten, president of the American Federation of Teachers.
"A strike is not a first resort for anyone. It's a last resort -- especially for teachers who are asked to do more with less every day," she said. "And enough is enough."