First and foremost: From kindergarten on, students spend thousands of hours studying subjects irrelevant to the modern labor market. Why do English classes focus on literature and poetry instead of business and technical writing? Why do advanced-math classes bother with proofs almost no student can follow? When will the typical student use history? Trigonometry? Art? Music? Physics? Latin? The class clown who snarks “What does this have to do with real life?” is onto something.

The disconnect between college curricula and the job market has a banal explanation: Educators teach what they know—and most have as little firsthand knowledge of the modern workplace as I do. Yet this merely complicates the puzzle. If schools aim to boost students’ future income by teaching job skills, why do they entrust students’ education to people so detached from the real world? Because, despite the chasm between what students learn and what workers do, academic success is a strong signal of worker productivity.

Suppose your law firm wants a summer associate. A law student with a doctorate in philosophy from Stanford applies. What do you infer? The applicant is probably brilliant, diligent, and willing to tolerate serious boredom. If you’re looking for that kind of worker—and what employer isn’t?—you’ll make an offer, knowing full well that nothing the philosopher learned at Stanford will be relevant to this job.

The labor market doesn’t pay you for the useless subjects you master; it pays you for the preexisting traits you signal by mastering them. This is not a fringe idea. Michael Spence, Kenneth Arrow, and Joseph Stiglitz—all Nobel laureates in economics—made seminal contributions to the theory of educational signaling. Every college student who does the least work required to get good grades silently endorses the theory. But signaling plays almost no role in public discourse or policy making. As a society, we continue to push ever larger numbers of students into ever higher levels of education. The main effect is not better jobs or greater skill levels, but a credentialist arms race.

Lest I be misinterpreted, I emphatically affirm that education confers some marketable skills, namely literacy and numeracy. Nonetheless, I believe that signaling accounts for at least half of college’s financial reward, and probably more.

Most of the salary payoff for college comes from crossing the graduation finish line. Suppose you drop out after a year. You’ll receive a salary bump compared with someone who’s attended no college, but it won’t be anywhere near 25 percent of the salary premium you’d get for a four-year degree. Similarly, the premium for sophomore year is nowhere near 50 percent of the return on a bachelor’s degree, and the premium for junior year is nowhere near 75 percent of that return. Indeed, in the average study, senior year of college brings more than twice the pay increase of freshman, sophomore, and junior years combined. Unless colleges delay job training until the very end, signaling is practically the only explanation. This in turn implies a mountain of wasted resources—time and money that would be better spent preparing students for the jobs they’re likely to do.

Edmon de Haro

The conventional view—that education pays because students learn—assumes that the typical student acquires, and retains, a lot of knowledge. She doesn’t. Teachers often lament summer learning loss: Students know less at the end of summer than they did at the beginning. But summer learning loss is only a special case of the problem of fade-out: Human beings have trouble retaining knowledge they rarely use. Of course, some college graduates use what they’ve learned and thus hold on to it—engineers and other quantitative types, for example, retain a lot of math. But when we measure what the average college graduate recalls years later, the results are discouraging, to say the least.