When a California judge struck down teacher tenure last week, union and government officials across the country got scared. How would the people running public school systems in America’s major cities defend a policy that, in the words of Los Angeles County Superior Court Judge Rolf M. Treu, "impose a real and appreciable impact on students' fundamental right to equality of education”?

When asked about the threat of a similar lawsuit in New York, Mayor Bill DeBlasio explained, “Retention [of teachers] has a lot to do with whether you have job security and a job future, where you can better yourself. . . .Tenure is a part of that.” If this is the best defense of tenure that the unions and the officials they helped elect can do, the unions are in trouble.

Having written an entire book about the arguments over tenure in higher education, I can say that college and university professors do a much better job of explaining the benefits of tenure in a way that suggests they have student interests in mind, not just their own. (Whether or not that’s true is another question.) When tenure is threatened, academics typically cry “academic freedom” almost immediately. While I don’t think the evidence shows that tenure has done a particularly good job of protecting academic freedom, at least there is the possibility that a student’s education might benefit if professors truly felt that they were able to engage in a freer exchange of ideas.

At the K-12 level, of course, since there is little in the way of publication and the vast majority of classes are not meant to cover controversial topics at all, it is hard to think of why teachers need the protections of academic freedom. And so the defense of tenure is as a job perk. Tenure is so you “can better yourself”—you being the teacher. It has nothing to do with the students. In higher education, the people who are at the top of the profession don’t care at all about tenure. It’s the people at the bottom who say tenure is the only reason they stick with the job.

But even if tenure is just a job perk and the idea is that you need it to attract top-quality professionals, well, how’s that working out for you? As the New York Post points out, “Barely two out of three of our city’s public-school students graduate high school in four years. Of those who do, just 31% are ready for a job or college.” Is the threat that if tenure is removed teaching is actually going to get worse? Hard to imagine.

Just as in higher education, guarantees of job security are not the way to encourage the brightest, most interesting and entrepreneurial minds to the profession. In fact, the tenure system at all levels of education works to discourage bright young people from entering the profession. In K-12 education, they know that seniority counts more than hard work. The people who want to enter jobs because they offer lifetime security are not the people we want teaching our kids.