American teachers in the past year have mounted the most sustained educator protest movement in decades. Their relentless string of mass walkouts continues this week in West Virginia, where education unions abruptly called a statewide strike Monday evening, and in California, which is bracing for a districtwide strike in Oakland on Thursday.

The movement started with cries for better pay and benefits for educators, and more funding for schools and classrooms. But it has evolved into a protest against the argument that has driven the bipartisan education reform agenda for the past two decades: that traditional public schools and the people who work in them are failing, and that they must be challenged by charter schools, private school vouchers, test-driven accountability and other forms of pressure to improve.

Here’s the latest on the teacher walkouts:

Why do teachers keep going on strike?

The teacher protest movement began in the run-up to the 2018 midterm elections. Educators in six conservative and swing states with weak unions — West Virginia, Kentucky, Oklahoma, Arizona, Colorado and North Carolina — thronged capitals to demand that politicians raise education budgets, sometimes by instituting new taxes.

Those protests won teachers a series of modest raises, but were less successful in pushing back against fiscal austerity more broadly. And though candidates who supported the walkouts won some state-level elections in November, the movement was not able to flip party control in red bastions like Arizona and West Virginia. That’s the major reason some of the same fights over local school funding, salaries and reform policies are still going on.

How has the movement changed?

The movement has entered a second phase, which began at the end of last year. Teachers led by strong unions organized strikes in a series of liberal cities. Those actions took place in Chicago charter schools and in Los Angeles, Denver and now Oakland.

The protest is no longer solely against the types of policies, like tax cuts and trimming budgets, that are supported by Republicans. With teachers pushing back against charter schools and other forms of school choice and competition embraced by some Democrats, the movement has taken on new life and may continue to spread.

Why are West Virginia teachers striking again?

Almost exactly one year after teachers in West Virginia kicked off the walkout movement, three state education unions called for a second walkout Monday night; it began Tuesday. Schools were closed in all but one of the state’s 55 counties.

This time, teachers protested a bill in the Republican-controlled Legislature that would have allowed public dollars to pay for private school tuition, and would have created up to seven charter schools. The bill would have also given teachers and other school workers a 5 percent raise, in addition to the 5 percent raise they won with last year’s walkout.

But organizers said getting a raise was less important than taking a stance against what they call school privatization. (Charter schools are publicly funded but privately managed.) They saw the Legislature’s action as retaliatory against their movement.

The bill was indefinitely tabled Tuesday, as teachers protested outside the Capitol.

The calling of a second state walkout within a year raises the question of whether educators will be able to sustain their energy and whether parents will be willing to put up with more school shutdowns.

What’s happening in California?

Several thousand teachers in Oakland expect to strike Thursday. The district has about 36,000 students, and the teachers union is pushing back against a proposal to shut down several dozen schools that serve predominantly black and Latino students. They are also asking for a raise, more charter school accountability and more funding for guidance counselors and nurses.

The Oakland Unified School District says it may be necessary to close schools because of a budget shortfall and declining enrollment. Families are leaving Oakland for the same reason teachers are dissatisfied with their pay: the Bay Area’s staggering housing costs, driven by the growth of the technology sector and a lack of new construction.

These issues are similar to those that prompted a weeklong strike in Los Angeles last month. That strike ended with the school board moving to slow the growth of the charter school sector.

Is there opposition to the movement?

Certainly — and not just among conservative budget-cutters. While many progressives applauded when some of the poorest-paid teachers in the country walked out of red-state classrooms last year, more recently, the strikes in Los Angeles and Denver revealed how deeply divisive education politics remain.

Many influential Democrats support the charter school sector and efforts to hold teachers accountable for students’ academic achievement. They see such policies as a civil rights imperative, since students of color and those from low-income families are the most likely to attend low-performing schools.

They have been frustrated to see their party’s presidential hopefuls line up to state their support for striking teachers — an indication of Democrats’ leftward shift on a host of issues related to the economy and inequality.

This article originally appeared in The New York Times.