DENVER (AP) — Tens of thousands of schoolteachers plan to walk off the job in Arizona and Colorado on Thursday, shuttering classrooms in pursuit of better pay and school funding.

But there are key differences between the protests in the two states, which share below-average spending on public schools. The actions build on a movement that spread from West Virginia, Oklahoma and Kentucky.

Here's a look at what's happening in Arizona and Colorado:

WHAT ARE TEACHERS PLANNING AND WHAT WILL HAPPEN?

Teachers will walk off the job to hold rallies and other demonstrations at their respective state Capitols.

In Arizona, the first-ever statewide strike starts Thursday after educators voted overwhelmingly in favor of the action. There's no end date scheduled, so it's not clear how long classes might be interrupted.

Educators who are planning to participate could face consequences in the right-to-work state, where unions do not collectively bargain with school districts and representation is not mandatory.

The Arizona Education Association, the largest teacher membership group, has warned its 20,000 members about a 1971 Arizona attorney general opinion saying a statewide strike would be illegal under common law and participants could lose their teaching credentials.

But no school district has said they would fire educators who strike or revoke teaching certificates.

In Colorado, teachers in four suburban school districts, including two of the largest in the state, will hold protests Thursday. But the bulk of the widespread walkouts will happen as a single-day demonstration Friday.

No laws in Colorado prohibit strikes. In response to recent national protests, a Republican lawmaker proposed a measure docking teacher pay and threatening fines and jail time for striking. Democrats oppose it, and it's not expected to pass the politically divided Legislature.

WHAT ARE THE DEMANDS?

Arizona teachers have a long list, including a 20 percent raise for teachers, who earn $47,403 annually compared with a national average of $59,660, according to 2017 data from the National Education Association. They also want yearly raises until their salaries reach the national average and competitive wages for classified staffers.

They are seeking a return to pre-Great Recession spending levels, which would be a roughly $1 billion increase annually, plus additional funding increases until Arizona reaches the national average in per-pupil spending.

In Colorado, teachers secured a $150 million annual boost to schools in this year's budget negotiations but want to wipe out an annual school funding shortfall within the next four years. After next year's boost, Colorado will underfund its schools by $672 million a year versus what's required by the state Constitution.

Colorado teachers don't have specific demands regarding salaries, because they are set at the local level. But the hope is that more state funding will trickle down in the form of better pay. The average Colorado teacher earned $51,808 in 2017, according to the national teacher salary data.

Complicating matters, lawmakers are negotiating sweeping changes to the state and school pension fund, which will likely cut teacher retirement benefits and could decrease their take-home pay. Educators say they hope their protests highlight that any changes to the pension fund could further erode their compensation.

HOW ARE STATE LEADERS RESPONDING?

Republican Gov. Doug Ducey of Arizona has offered teachers a 20 percent raise by 2020 and pledged to see his proposal through despite concerns on how to fund it.

Ducey's plan relies on higher-than-expected state revenue. Republican legislative leaders have questioned where the money might come from and are negotiating the plan this week.

Colorado lawmakers have secured a bipartisan deal to boost school funding but are negotiating on the pension changes. Republicans want public employees, including teachers, to put more of their own pay into the system to close a $32 billion funding gap. Democrats have countered with a plan to contribute $225 million in annual state funding to shore up the fund.

WHAT DOES THE WALKOUT MEAN FOR SCHOOLS, TEACHERS AND PARENTS?

In both states, school districts have been weighing whether to stay open or cancel classes.

Many in Arizona, including the state's largest district in suburban Phoenix, will be closed at least Thursday and Friday. Some have said they will try to stay open if they have enough staff.

Many parents are scrambling to make child care plans. Community groups are organizing day camps, churches are opening for free care and some stay-at-home parents are volunteering to watch others' children.

Colorado's largest district, Denver Public Schools, will be closed Friday, along with more than a dozen others. Four others, including large suburban districts in Jefferson and Douglas counties, will be shuttered Thursday but are expected to reopen Friday.