Education, Betsy DeVos once said, is an “industry.” “It’s a battle of Industrial Age versus the Digital Age. It’s the Model T versus the Tesla. It’s old factory model versus the new internet model. It’s the Luddites versus the future,” she told a SXSWEdu audience in 2015. Three years later, she’s the secretary of education, and the so-called industry she presides over is undergoing a period of mass activism. Teachers in Oklahoma, Kentucky, and Arizona are threatening to emulate their West Virginia peers, who staged a historic strike earlier in March. Students, too, have grievances: On March 14, students in over 2,500 high schools and colleges, most of them public, will walk out of class to call for gun regulation.

DeVos’ belief—that education is an industry, improved by competition—is shared by other school choice advocates. But it also pits her against the very idea of public education, one of the bedrock principles of the American project to provide equality to all. The Constitution may not recognize a right to an education, but some states do, and each state constitution includes language requiring the creation of a public school system. That language can vary widely, but there are commonalities; the words “free,” “common,” and “efficient” frequently appear.

Free, common, and efficient. These words tell us that public schools should be accessible and ubiquitous, and that they should function. The teachers’ strikes may be clouded in the language of fiscal austerity, and current student walkouts may react to the different threat of gun violence, but they both stand against those who would undermine the pillars of the public school system. If there is a unifying theory linking student walkouts to teacher strikes, it’s this: Public schools are some of the most democratic institutions in America. At a time when public welfare, another democratic principle, looks shakier than ever, it’s nearly a miracle that entry is still free, and that schools are, theoretically at least, open to all.

Of course, public schools bear the marks of prejudice, from the school-to-prison pipeline to the de facto segregation of the school system in certain parts of the country. But that only underscores the public school’s historic role in the fight for equality—as well as the anti-democratic nature of the campaign to privatize public education, whether it’s in the form of vouchers or starving educators of funds. If America still has a public square, it isn’t located in the balkanized press or the halls of Congress, but in public schools.

In the battleground of American politics, public schools are a regular flashpoint. Charged with the education, and presumably the character development, of the country’s youngest citizens, public education is not only about endowing them with the skills necessary to participate in the workforce, but also grounding their relationship with the state in certain political terms. Political strife thus repeatedly spills over into American public schools: In 1844, to name one example, rising anti-Catholic nativism spurred public riots over which Bible Philadelphia students could read in public schools—if they were going to read the Bible at all.

Religion is a frequent catalyst for public school activism, as is racial injustice. The democratic promise of public education is one that states, despite their lofty constitutions, have at times refused to fulfill. (Alabama’s constitution still stipulates that public schools should be segregated.) When states betray schools, they betray students and teachers. Students, inspired by Parkland’s newly minted gun control activists, will remind the country of this on Wednesday.

They’ll be joining a much older history of activist struggle in public schools. Before Parkland there was Ferguson, and before Ferguson there was Prince Edward County, Virginia. There, in 1951, 16-year-old Barbara Johns led a walkout to protest the conditions in her segregated high school. That walkout led to a lawsuit, which in turn became part of Brown v. Board of Education. Post-Brown, Prince Edward County schools closed rather than integrate, and only re-opened after another Supreme Court verdict in 1964.

Student protest, then, not only helped defeat segregation initially; it repeatedly forced the issue until the South nominally de-segregated its schools. Johns’ walkout wasn’t an isolated incident: In 1963, one year before Prince Edward County reopened, around 1,000 black children in Birmingham, Alabama, walked out of class and marched downtown to protest civil rights violations; they were attacked and arrested by Bull Connor’s police force.

Five years later, in 1968, Mexican-American students walked out of their Los Angeles high schools en masse. Though they didn’t experience segregation de jure, they did, like African-American students in the Jim Crow South, endure racism, overcrowding, and collapsing facilities. In what The Los Angeles Times recently termed “the first act of mass militancy by Mexican Americans in modern California history,” students demanded smaller classes, an end to corporal punishment, and the introduction of classes on Mexican-American history and culture.

“Before the walkouts, no one cared that substandard schools made it all but impossible for Chicano youths to find strength and pride in their culture, language, and history—or to make the most of their lives,” David Sanchez, founder of the Brown Berets, told the Times. The walkouts galvanized the Chicano power movement. The Times reports that the Los Angeles school district eventually granted two student demands: smaller class sizes and the hiring of more bilingual personnel. And despite a major crackdown by police, Mexican-American admissions to UCLA soared starting a year later.

Teachers, meanwhile, have been organizing for over a century, for equal pay for equal work and for collective bargaining rights. Contemporary walkouts, either realized or proposed, often follow in the steps of previous direct actions. Teachers in both West Virginia and Oklahoma went on strike in 1990. West Virginia walked out again this year, this time in a coordinated, statewide move, and Oklahoma is on track to do the same on April 2.

The interests of students and teachers don’t always align. For some students, especially students of color, teachers are complicit in over-policing. Liberal school reformers say sclerotic teachers unions have obstructed student progress—rhetoric they use to promote a different privatization agenda. But public education, at its best, creates a true public square, where an absence of security or an absence of decent wages can be named as injustices. Individuals who don’t have access to Congress or to media platforms or money do generally have access to one last engine of influence: A system of free, common public schools.

No wonder Betsy DeVos prefers private options. You can hide all kinds of injustice in the dark.