Ian Haney Lopez, a law professor at the University of California at Berkeley, in the NYT (May 22, 2004):

With commemorations from coast to coast to remind them, most Americans already know that this week was the 50th anniversary of Brown v. Board of Education. Unfortunately, what they don't realize is that the country missed an equally important anniversary two weeks ago, that of Hernandez v. Texas — the perennially overshadowed antecedent to Brown that was decided on May 3, 1954.

That case merits commemoration not just because the Supreme Court used it to finally extend constitutional protection to Mexican-Americans, important though that is, especially now that Latinos are the largest minority group. It's worth celebrating because Hernandez got right something that Brown did not: the standard for when the Constitution should bar group-based discrimination....

Because both sides insisted that Mexican-Americans were white, Hernandez v. Texas forced the court to confront directly a question it would sidestep in Brown: under precisely what circumstances did some groups deserve constitutional protection? Hernandez offered a concise answer: when groups suffer subordination.

"Differences in race and color have defined easily identifiable groups which have at times required the aid of the courts in securing equal treatment under the laws," the court wrote. But, it said, "other differences from the community norm may define other groups which need the same protection." Succor from state discrimination, the court reasoned, should apply to every group socially defined as different and, implicitly, as inferior. "Whether such a group exists within a community is a question of fact," the court said, one that may be demonstrated "by showing the attitude of the community."

How, then, did the Texas community where Hernandez arose regard Mexican-Americans? Here the court catalogued Jim Crow practices: business and community groups largely excluded Mexican-Americans; a local restaurant displayed a sign announcing "No Mexicans Served"; children of Mexican descent were shunted into a segregated school and then forced out altogether after the fourth grade; on the county courthouse grounds there were two men's toilets, one unmarked and the other marked "Colored Men" and "Hombres Aquí" ("Men Here").

The same sort of caste system that oppressed blacks in Texas also harmed Mexican-Americans. But it was Jim Crow as group subordination, rather than as a set of "racial" distinctions, that called forth the Constitution's concern in Hernandez v. Texas.