The evidence on rising costs is well established: From 2000 to 2016, the tuition-and-fees component of the Consumer Price Index rose 3.54% annually (74.5% over the entire period), adjusting for overall inflation. With sluggish business investment, a slowdown in income growth has aggravated the rising burden of paying for higher education. American families have taken on more than $1.3 trillion in student-loan debt—more than what they borrow with credit cards or to buy cars.

Less well known is that the earnings advantage associated with a bachelor’s degree compared with a high school diploma is no longer growing like it once did. Census data show that the average annual earnings differential between high school and four-year college graduates rose sharply, to $32,900 in 2000 (expressed in 2015 dollars) from $19,776 in 1975—only to fall to $29,867 by 2015. In the late 20th century rising higher-education costs were offset by the increasing financial benefits associated with a bachelor’s degree. Since 2000 those benefits have declined, while costs have continued to rise.

Rising costs and declining benefits mean the rate of return on a college investment is starting to fall for many Americans. Some observers have begun asking whether it might not be better for more students to forgo college in favor of less expensive postsecondary training in vocations like welding and plumbing. The New York Federal Reserve Bank says about 40% of recent college graduates are “underemployed,” often for a long time. They sometimes resort to taking jobs as Uber drivers or baristas. With some inexpensive vocational training, they could easily get jobs that pay much better.