Teachers walk off the job in Arizona, Colorado to protest shrinking paychecks

• Teachers across the country are walking off the job in many states to protest shrinking paychecks.
• Teachers marched to the Arizona state Capitol Thursday for a walkout that closed most of the state's public schools as teachers in neighboring Colorado staged a similar rally in Denver.

AAron Ontiveroz | Denver Post | Getty Images

Educators gather en masse wearing red and holding signs during a teachers rally for more educational funding at the Colorado State Capitol on Thursday, April 26, 2018.

There's a simple reason teachers across the country are walking off the job: in many states, their paychecks are getting smaller.

The latest protests brought a wave of red-clad teachers to the Arizona state Capitol Thursday for a walkout that closed most of the state's public schools as teachers in neighboring Colorado staged a similar rally in Denver.

Thousands of teachers were expected to march through Phoenix to demand a 20 percent raise for teachers, about $1 billion to return school funding to pre-Great Recession levels and raised pay for support staff, among other things.

The walkouts are part of a widening protest that began earlier this year with a grass-roots movement known as #RedforEd that sparked teacher walkouts in West Virginia, Oklahoma and Kentucky.

Across much of the country, a decade-long economic recovery has created millions of new jobs and begun to nudge average wages higher. While the median household income stagnated in the years immediately following the Great Recession, paychecks have begun rising again for most Americans.

But in more than half of the states, teacher salaries have fallen, in some cases sharply. As of the 2016-2017 school year, the latest data available, the average inflation-adjusted salary for elementary and secondary school teachers was lower than it was nearly two decades earlier.

Teachers in Colorado and Arizona have been among the hardest hit, according to data from the National Center for Education Statistics.

Though some states have begun boosting teacher salaries, the overall level of education funding hasn't yet recovered from the deep cuts seen after the Great Recession hit in late 2007, much of which came from cuts in state funding.

But while the economic recovery has helped most states restore their overall fiscal health, funding for education continues to lag below levels seen before the recession hit.

In Colorado, for example, lawmakers from both parties have agreed to give schools their largest budget increase since the Great Recession. But teachers say the state has a long way to go to recover ground lost during the recession - and before - because of the state's strict tax and spending limits.

And because the Colorado legislature can't raise taxes without consulting voters first, they're not expecting an immediate fix. The teachers' union is backing a ballot initiative to raise taxes on people earning more than $150,000 a year and corporations.

In Arizona, Education Association president Joe Thomas said he doesn't expect an early end to Thursday's walkout.

Republican Gov. Doug Ducey has backed a plan to raise teacher salaries by 20 percent by 2020. But organizers of Arizona's #RedforEd movement say the governor's plan relies on rosy revenue projections and could leave other education funding needs unmet.

More than 840,000 Arizona students are expected to be out of school Thursday, according to an analysis from the Arizona Republic and could be out longer. The state Department of Education said the state has more than 200 districts and more than 1.1 million school children.

(The Associated Press contributed.)

WATCH: AFT's Weingarten on public school funding crisis