Tenure remains common in schools around the world, but since 2009, two-thirds of American states have weakened their teacher-tenure laws in response to President Obama’s Race to the Top program. California, where Governor Jerry Brown is far more sympathetic to the teachers unions than most governors, was not among them. The Vergara ruling is an especially big blow to unions on typically sympathetic turf.

Judge Rolf Treu’s decision will not take effect while the California Teachers Association mounts an appeal. Depending on the outcome of that effort, his ruling may or may not ever impact the lives of California teachers. But the ruling’s rhetoric is stern and memorable stuff, borrowed directly from the playbook of the Silicon Valley philanthropists and deep-pocketed advocacy groups that bankrolled Vergara. Citing familiar economic research showing that great teachers increase their students’ annual earnings by 1.3 percent, Judge Treu wrote that “grossly ineffective teachers substantially undermine the ability of [a] child to succeed in school. … The evidence is compelling. Indeed, it shocks the conscience.” Ending tenure and other seniority protections for teachers, he ruled, would protect the civil rights of California’s poor children to “basic equality in public education.”

Is the premise of Treu’s ruling correct? Will axing tenure and seniority lead directly to better test scores and higher lifetime earnings for poor kids?

Here’s where the judge is right: It is difficult—actually, close to impossible—to argue that California’s teacher-tenure system makes sense. Research shows that most first-year teachers are mediocre at best. But good teachers tend to make huge jumps in effectiveness by the end of their second year on the job, and those improvements are often visible through classroom observation and students’ rising test scores. Yet California evaluates teachers for tenure in March of their second year of work, before two full years of student-teacher data are available.

This means that under current California law, principals are forced to make high-stakes decisions about teachers without enough evidence. This disadvantages students, who might get stuck with sub-par instructors, but it also hurts teachers, who aren’t given enough time to prove their skill. Once a teacher earns tenure, it can cost tens or even hundreds of thousands of dollars—and countless administrative and legal man-hours—for a district to permanently remove him from his job. And in the event of budget cuts or school closings, California law mandates that the least experienced teachers be laid off first, even if they are more effective than their older colleagues, a policy known as “LIFO,” or “Last In, First Out.”

California is an outlier. Only 12 states have formal laws on the books mandating LIFO. Nationally, teachers work an average of 3.1 years before they become eligible for tenure. Not even teachers support the idea of tenure after less than two years on the job. A 2012 survey of 10,000 teachers found that, on average, they believed it was reasonable to work 5.4 years before being evaluated for tenure. As Treu noted in his ruling, the arguments in Vergara revealed remarkable consensus between the prosecution and defense on the fact that California’s tenure policies are far from best practices.