At first glance, the scene probably looks familiar to many people in Phoenix: tens of thousands massing outside Chase Field on a bright Thursday afternoon in April, clad in red and rippling with anticipation. But that scene, if it were typical, would feature fans of the Arizona Diamondbacks — not the teachers who have gathered near the baseball stadium with quite another event in mind.Educators across Arizona walked out of their classrooms Thursday with a series of demands in hand, foremost among them a raise and a return to the school funding levels of a decade ago. And many of those walking out have descended on downtown Phoenix, where they plan to march from Chase Field to a rally outside the state Capitol. Organizers expect from 30,000 to 50,000 teachers and their supporters to attend.Meanwhile, scores of public school districts and charter schools have shuttered for the day for lack of staff. According to an analysis by The Arizona Republic, more than 840,000 of 1.1 million students — or about 75 percent statewide — have been affected by the closures."I think our students understand that we need a change and enough is enough," Noah Karvelis, a teacher and organizer of Arizona Educators United, or AEU, said at a news conference Wednesday ahead of the rally. The grass-roots group is behind #RedforEd, the movement calling on teachers and their supporters to wear red in solidarity."We simply can't take it any longer," Karvelis said.At the protest's heart are escalating frustrations with pay and financial support for schools — similar to those that have motivated teachers in several other states to walk out since a showdown in West Virginia ended with a salary bump for educators there. In Colorado, teachers are also mounting protests Thursday and Friday, which have already resulted in the closure of a handful of that state's large school districts.In Arizona, specifically, the AEU has announced five central demands — among which are 20 percent raises for teachers and certified staff in the next school year, smaller class sizes, and yearly bumps in pay until the state reaches the national average salary, which hovers at nearly $59,000 per year for public school teachers.Currently, Arizona's average stands at just over $47,000, according to the National Center for Education Statistics.The state's governor, Doug Ducey, has proposed a 20 percent pay raise for Arizona teachers by 2020, saying, "This raise is earned, and it is deserved.""To parents, I understand the pain and pressure caused by today's strike. I want you to know, I am working to get this 20 percent raise passed at the Legislature. But we need your help to make it a reality," he said in a statement Thursday, encouraging parents to contact their legislators over the matter.Yet the protesting teachers have already rejected this proposal, calling it unsustainable as it is currently drawn up. Teachers' groups, including the Arizona Parent Teacher Association, argue that under the plan the raise would simply cause woes for others in the state's educational system."I believe that the people are with us, and that provides the public pressure to get the governor to move," Arizona Education Association President Joe Thomas said Wednesday, according to the Republic newspaper.In this respect, an NPR/Ipsos poll released Thursday appears to back him up. Nearly two-thirds of respondents approved of national teachers unions, and three-quarters said teachers have the right to strike.In Phoenix, meanwhile, the protesters plan to ensure their demands are heard Thursday — literally, in fact. The demonstrators are wrapping up their march outside the state's legislative buildings, where they are holding a rally right outside lawmakers' offices. Copyright 2018 NPR. To see more, visit https://www.npr.org/.