Denver's first teachers' strike in a quarter of a century is the result of 11th-hour negotiations that collapsed over the weekend.
Cordova said students at schools she visited were working in classrooms, overseen by adults.
Nick Onofrio, a parent of a third-grader said he is disheartened by the hostility expressed between the union and the school district.
However, Polis said the state could decide to intervene - and suspend the strike for up to 180 days - if a walkout dragged on. The district proposal raises that to $45,500, but teachers want $45,800.
One student, Matt Pence, told the Denver Post that students were supposed to follow special schedules amid the strike.
In one school, students danced and chanted in the hallways as they walked out to demonstrate to support their teachers.More news: Teenager, 18, finally gets vaccinations and attacks his anti-vaxxer parents
Many drivers honked in support and used their cellphones to capture the moment. Instead, classes will be staffed by administrators and substitute teachers.
Some teachers have become ineligible for bonuses after their schools lost their official low-income status as parts of the city undergo gentrification.
According to district data, that's about half of the teachers employed.
Denver's teachers started picketing before the start of the school day and students crossed through the picket lines on their way to class in some locations.
Chicago's 2012 teacher strike, which like Denver's reflected resistance against a certain brand of education policy as much as a bid for improved compensation, lasted seven school days.
House Majority Leader Alec Garnett said Monday lawmakers must find a way to fix conflicting laws that restrict state K-12 spending by hundreds of millions of dollars a year. An additional 1,400 administrators are also ready to help out where needed at the schools. Teachers say the reliance on bonuses leads to high turnover, which they say hurts students, and that spending money on smaller class sizes and adding support staff, like counselors, is the best way to help disadvantaged students.
CNN shared stories on Monday of the struggles of some Denver teachers, including a physical education teacher who drives a Lyft on off-hours to cover his bills, a Spanish teacher who hasn't made enough in nine years of teaching to start a savings account, and two teachers who are considering leaving the field because they can't afford to live on their paltry salaries. The strike is estimated to leave 92,000 students over 160 public schools without their teachers for an unknown period of time, The Post reported. But canceled classes for 5,000 preschool children were canceled because the district does not have the staff to take care of them. This follows strikes by tens of thousands of educators a year ago in Arizona, West Virginia, Kentucky, North Carolina, Washington state, and in the cities of Jersey City, New Jersey, and Pueblo, Colorado. This keeps base pay at an average of $43,255 per year, according to USA Today-an amount that makes it hard for many to make ends meet in Denver.More news: Georginio Wijnaldum reveals extent of his illness before Liverpool victory
Another negotiation session is expected on Tuesday.
Teachers picket outside East High School.
In anticipation of a strike, the school district hired 300 new substitute teachers to bolster its roster of 1,200 subs, the Post reports.
The teachers' union says 93 percent of participating members backed a strike in a vote last month. Denver teachers are planning to strike Monday, Feb. 11, 2019 after failed negotiations with the school district over base pay.
Teachers are claiming the district's proposal lacks transparency and "pushes for failed incentives for some over meaningful base salary for all".
"Offers our teachers an nearly 11-percent increase for next year and to hear the feedback and to be in a position that, rather than sticking with it and figuring out, I'm incredibly disappointed that they walked away", stated Susana Cordova, DPS superintendent.More news: How Toro Rosso's design gap to Red Bull is closing - F1