Brown v. Board of Education was the landmark Supreme Court case that ended racial segregation in schools in 1954. But it wasn’t the first to take on the issue. Eight years earlier, in 1946, a group of Mexican American families in California won the very first federal court case ruling that segregation of public schools was unconstitutional.

Unlike the segregation of African Americans in the “Jim Crow” South, segregation of Mexican Americans in California wasn’t dictated by law. But starting in the 1920s, when waves of Mexican laborers arrived to work the citrus groves of Southern California, California communities began to enforce their own de facto segregation.

Restaurants posted signs in their doors reading, “No dogs or Mexicans." At movie theaters, Mexican Americans had to sit in the balcony, not the lower level. Public swimming pools had “Mexican Mondays” after which the pool was drained and cleaned before Anglo residents would step foot in it again.

The same de facto segregation existed in California public schools. By 1940, more than 80 percent of Mexican American students in California went to so-called “Mexican” schools, even though no California law mandated such a separation. (Legal segregation in California schools did exist for two other groups: Asian Americans and Native Americans.)

California school boards claimed that they put Mexican Americans in their own schools in order to help them. They used culturally biased I.Q. tests to argue that Mexican American students needed specialized instruction in English and other subjects. The school boards argued that students of Mexican heritage would “Americanize” faster if taught separately.

At the time, segregated schools were supposed to abide by the “separate but equal” clause established in 1896 by Plessy v. Ferguson. But just as in the segregated South, the “Mexican” schools in California were in terrible condition compared to the “American” schools. And instead of receiving specialized instruction to improve their language and academic skills, Mexican American students were trained to become field workers and house cleaners. Most of the school board members were wealthy citrus farmers whose livelihoods depended on Mexican American labor.

“It was very much in the economic interest of the agricultural elite and the Anglo community at large to keep these people in a second-class position,” says Philippa Strum, a Global Fellow at the Woodrow Wilson Center for Scholars, who wrote a book on the Mexican American anti-segregation movement in California.

The Mexican schools started two weeks late every fall so that children could join their parents in the walnut harvest. They’d arrive at school with their palms dyed black from the work. During the citrus harvest, school would run from 7:30 a.m. to 12:30 p.m. so that students could still work in the orchards.

The Mexican and American schools were often side by side, separated only by a field or an electrified fence. The Mexican American kids held recess in an empty, dirt-floored lot in plain sight of the sparkling playground at the American school.

Eventually, Mexican American families in many California communities had enough. In a model of resistance that would be echoed in later anti-segregation movements, they took the schools to court. In fact, the very first legal victory against segregation in America was in San Diego County in 1930, when Mexican American parents in the Lemon Grove School District organized a boycott and successfully sued the schools for integration.

But the Lemon Grove decision only applied in one school district. It would take another group of Mexican American parents to strike down segregation statewide.

Gonzalo and Felicitas Mendez and their children moved to the small town of Westminster outside of Los Angeles in 1944. The Mendez family tried to enroll their kids at the local 17th Street School but were turned away. (Their in-laws, who were also of Mexican heritage but had lighter skin and the “European” surname Vidaurri, were accepted.)

Gonzalo Mendez insisted that not only his children, but all Mexican-American students be given a quality education equal to their Anglo neighbors. When the school board refused to change its policies, Gonzalo joined four other plaintiffs—William Guzman, Frank Palomino, Thomas Estrada and Lorenzo Ramirez—from nearby Santa Ana County school districts and filed a lawsuit in federal district court known as Mendez v. Westminster.

In the Mendez case, attorney David Marcus saw an opportunity to defeat segregation in California for all students of color, including Asian Americans and Native Americans. He called a number of powerful witnesses to the stand, including Mexican American schoolchildren who testified of the poor conditions in their schools, and social scientists who provided evidence on how feelings of inferiority negatively impacted learning and development.

The case was heard in 1946 by Federal District Judge Paul McCormick, who delivered a landmark ruling that segregation of Mexican Americans was not only unenforceable under California law, but it violated the equal protection clause of the 14th Amendment to the U.S. Constitution.

“A paramount requisite in the American system of public education is social equality,” wrote Judge McCormick. “It must be open to all children by unified school association regardless of lineage."'

The Santa Ana school districts immediately appealed the decision, setting up a rematch in the Ninth Circuit Court of Appeals in San Francisco. When the NAACP heard about Judge McCormick’s decision, which directly challenged the constitutionality of race-based school segregation, it saw a strong test case for challenging segregation nationwide.

Even though Thurgood Marshall’s name was on the amicus brief filed by the NAACP in the Mendez trial, it was his assistant special counsel Robert Carter who drew up the arguments.

“Robert Carter later described his brief in the Mendez case as a trial run for what became Brown v Board of Education,” says Strum. “The whole idea that educational segregation necessarily implied inferiority and therefore interfered with the ability of students to learn. That’s what was in the brief here and that was the basis for the NAACP’s argument in Brown.”

The Ninth Circuit ruling in 1947 was another victory for Mendez and his fellow plaintiffs, but not nearly the slam dunk that the anti-segregation movement hoped it would be. The court struck down segregation in the Santa Ana County schools, but not because it violated anyone’s 14th amendment rights on the basis of race or ethnicity. Segregation of Mexican-Americans simply wasn’t the law in California, so it wasn’t allowed.

The Ninth Circuit decision even left open the possibility that the California legislature could pass a segregation law expressly targeting Mexican Americans, just like the laws already on the books for Asian Americans and Native Americans.

But just the opposite happened. Taking his cue from Judge McCormick’s earlier opinion, California Governor Earl Warren decided to outlaw school segregation of any kind in the state. Seven years later, Warren was Chief Justice on the Supreme Court when it heard Brown v. Board of Education.

So why was Mendez v. Westminster, despite its precedent-setting decision, largely lost to legal history? For one thing, the case never made it to the Supreme Court, so its impact was only felt in California. And ultimately, the early victory by Mexican American families in California was overshadowed by the historic nature of Brown v. Board of Education.

Strum, who taught constitutional law for 35 years, had never even heard of Mendez v Westminster until the U.S. Postal Service issued a stamp commemorating the landmark Civil Rights decision in 2007. Four years later in 2011, the Mendez’ daughter, Sylvia Mendez, received the Presidential Medal of Freedom from President Barack Obama.

“When I got it I couldn’t stop crying, because I was thinking finally my mother and father are getting the thanks they deserve,” Mendez told the Los Angeles Times in 2016. “This is theirs, not mine. They stood up against the establishment.”