In early May, Detroit teachers staged a “sick-out” to protest the inability of the strapped school district to make payroll. A month before that, Chicago teachers held a one-day strike for similar reasons. As unionization in the private sector declines, teachers and other public-sector employees are often the most visible representatives of the modern labor movement.

But public employees are relative newcomers to U.S. unions. In a paper for The History Teacher, Robert Shaffer notes that many of us didn’t learn about the rise of unions representing teachers and municipal workers in history class. Which is a shame, because it’s a dramatic story that has had big effects on the country.

In 1955, Schaffer writes, there were 400,000 members of public employee unions in the U.S. By the 1970s, the number had risen tenfold, to more than 4 million.

The sudden advent of public-sector unionism was partly a product of legal changes. In 1962, President John F. Kennedy issued an executive order allowing federal workers to unionize, and some states and cities followed suit. But, in many cases, it was only militant—and illegal—action by teachers and other public-sector workers that forced politicians to change laws.

The rise of public-sector unions was closely tied to other social movements. Martin Luther King Jr. endorsed a unionization fight by Philadelphia teachers in 1965. That same year, municipal hospital workers in New York City—most of them African American—organized in a campaign that drew on the traditions of both private-sector unionism and the Civil Rights movement. And, of course, at the time of his death, King was in Memphis to support a strike by public-sector sanitation workers.

The feminist movement was also part of the activism among public workers, particularly in the traditionally female profession of teaching. Unionization was an obvious route toward the goal of equal pay for women’s work, and public-sector unions were—and still are—more likely to be led by women than their private-sector counterparts.

In the 1960s, strikes by teachers and other employees were generally illegal. But that didn’t stop them. In 1968 alone, strikes closed schools in Cincinnati, Pittsburgh, San Francisco, Washington D.C., Albuquerque, and Montgomery County, Maryland. In Florida, nearly half the teachers across the state—teachers responsible for a half million students—walked out for three weeks. Beyond seeking higher pay and the recognition of their unions, the teachers’ strikes called for smaller class sizes and better conditions for student learning.

Despite the decline of the broader labor movement since then, teachers continue to fight that same fight.

MORE STORIES ABOUT UNIONS

Why Should We Care About the Death of Labor Unions?

Labor Unions, Public Employees, and Race: And Interview with William P. Jones

Scott Walker, Labor Unions, and the Right to Work