The Boulder Valley School District is joining other area districts in canceling classes on Friday as thousands of teachers plan to join a rally at the state Capitol to call for more funding for education.

Boulder Valley Superintendent Cindy Stevenson sent an email to families and staff members on Monday afternoon, saying enough teachers requested time off that “we will simply not be able to provide a safe and effective learning environment for all of our students.”

The Colorado Education Association is organizing the statewide teacher rally, with the union representing Denver classroom teachers saying it plans to walk out midday Friday to rally at the Capitol early in the afternoon.

The neighboring St. Vrain Valley, Adams 12 and Thompson school districts all announced last week that they were canceling classes because of expected high teacher participation rates.

Altogether, nine of the state’s 10 largest districts now have canceled classes either on Thursday or Friday for the planned rallies.

Tina Mueh, the Boulder Valley Education Association’s president, said local teachers want to support teachers throughout the state who don’t enjoy the same support from their districts and communities.

“What we have here is in contrast to the professional situation as so many of their colleagues,” she said.

That support includes salaries that are among the highest in the state and a community that’s approved multiple tax increases.

Last week, teachers in Boulder Valley were planning to mainly participate in walk-ins at their schools to show solidarity with those walking out to lobby in Denver.

But interest in joining the walkouts increased over the weekend, with enough teachers — more than 300 — taking the day off that the district decided to cancel classes, officials said.

Sports practices and games are expected to continue as planned. The “SAC” and “YMCA” after-school child care programs are expected to run as scheduled, but morning child care programs and kindergarten enrichment will be canceled.

Boulder Valley’s Stevenson said in her letter that she fully supports teachers speaking out on school funding issues.

“I personally want you to know that the Board of Education, my leadership team and I value our educators,” she wrote. “We have been heavily engaged in the state-wide discussions on increasing funding and equity this year.”

Colorado consistently ranks in the bottom tier for school funding and teacher pay, though there is considerable variation around the state.

A recent study ranked Colorado last for the competitiveness of its teacher salaries, and nearly half the state’s districts are now on four-day weeks.

The 2018-19 budget takes a big step toward restoring money cut during the Great Recession, but the state is still holding back $672 million from what it would have spent on K-12 education if it complied with constitutional requirements to increase per-pupil spending at least by inflation each year.

Chalkbeat Colorado contributed to this report.

Amy Bounds: 303-473-1341, boundsa@dailycamera.com or twitter.com/boundsa