Bryan Caplan explains (in The Case Against Education) why vocational education rules:
In proponents’ eyes, vocational education raises pay, reduces unemployment, and increases high school completion. Research, though a bit sparse, supports proponents on all counts. Core insight: vocational students are typically “academic underachievers” before entering the vocational track. The right metric isn’t, “How do vocational students compare to average students?” but rather, “How do vocational students compare to comparable students who didn’t study a trade?” Vocational ed fares well by this metric. It raises pay more than academic coursework. It reduces unemployment more than academic coursework. It even boosts high school graduation: the academically uninclined are less prone to quit school when they don’t detest all their classes. Vocational education even seems to deter crime. Those who search for the most lucrative mix of academic and vocational education normally discover students are too academic for their own good. Most will earn more if they replace some—but not all—of their standard courses with vocational alternatives.
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What fraction of vocational ed’s selfish benefits stem from signaling? The lowest estimates, strangely, come from vocational education’s critics. Many inadvertently set its signaling share below zero. How so? Critics fear that vocational education bears a stigma.
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In this scenario, vocational education enriches society more than it enriches vocational students. Society gains the extra productivity, but students capture the extra productivity less the stigma.
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Vocational ed stands out because it prepares students for common jobs. According to the Bureau of Labor Statistics, the United States has roughly 900,000 carpenters, 700,000 auto mechanics, and 400,000 plumbers. Classic college-prep classes like literature, foreign language, and history fall short because they prepare students for rare jobs. The whole U.S. employs only 129,000 writers, 64,000 translators, and 3,800 historians.
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Conventional education mostly helps students by raising their status, but average status cannot rise. Vocational education mostly helps students by building their skills—and average skill can rise.