The General Educational Development tests, currently a battery of five exams, were developed 72 years ago as a way for high school dropouts who had served in the military to prove their math and reading skills. If they passed, they’d earn a high school equivalency diploma, which in turn would give them access to higher education and better jobs. Seems like a good idea, right? Not according to James Heckman, a Nobel Prize–winning economist at the University of Chicago. “The GED [is] not really that effective,” he says.

In the new book The Myth of Achievement Tests: The GED and the Role of Character in American Life, Heckman and two of his graduate students, John Eric Humphries and Tim Kautz, cite decades of research showing that the typical holder of a high school equivalency diploma doesn’t earn any more than the typical high school dropout.

Even worse, they argue, the GED encourages students who have the cognitive skills to graduate to leave school early. Consider that it generally takes 32 hours to study for the test compared with thousands of hours to earn a high school diploma. Which do you think most teenagers would prefer? No wonder nearly a quarter of the nation’s 673,000 GED recipients in 2012 were 18 or younger (the minimum age varies from state to state).

Heckman and his students make the case that as more states began accepting the GED (41 of them, including Illinois, now do), they created a hidden class of high school dropouts, one concentrated among minorities. (Sixty percent of Illinois’s 25,000 GED test takers in 2012 were nonwhite.)

When Heckman’s team adjusted American high school graduation rates to count GED holders as dropouts instead of graduates, they found that the black-white graduation gap—15 percent 35 years ago—hasn’t closed at all. And the overall graduation rate has actually decreased in the past half century, from 80 percent to 75 percent. “If we take the GEDs as the high school equivalent, we delude ourselves in thinking that American society is doing better than it is,” Heckman says.

Making the test more difficult does seem to lower dropout rates. In 1997, the American Council on Education—which creates and administers the test—tightened its scoring. Since then, dropout rates have fallen 1.3 percent overall. Among 12th graders, they fell 3 percent.

In January, Illinois, along with several other states, adopted an even harder GED test. (It includes more demanding math problems, for example.) The state also imposed a higher barrier to entry, raising the test fee from $50 to $120. These changes may help somewhat, but they don’t go far enough, Kautz says. They don’t “send a different signal,” as he puts it.

He and his colleagues advocate imposing a different barrier: raising the minimum age of GED test takers from 17 in Illinois to 19 or 20. He also recommends options such as apprenticeship programs, which are common in Europe, to address the “character deficits” that lead capable students to drop out. Heckman says, “If you look at programs that essentially integrate school and work, that can be very effective.”

It’s a compelling argument. The impulsive late-teen years are a perilous time to present a mirage of freedom.