It’s a cruel irony that a college degree is worth less to people who most need a boost: those born poor. This revelation was made by the economists Tim Bartik and Brad Hershbein. Using a body of data, the Panel Study of Income Dynamics, which includes 50 years of interviews with 18,000 Americans, they were able to follow the lives of children born into poor, middle-class and wealthy families.

[Read the Op-Ed from Tim Bartik and Brad Hershbein on the value of a degree, “College Does Help the Poor.”]

They found that for Americans born into middle-class families, a college degree does appear to be a wise investment. Those in this group who received one earned 162 percent more over their careers than those who didn’t.

But for those born into poverty, the results were far less impressive. College graduates born poor earned on average only slightly more than did high school graduates born middle class. And over time, even this small “degree bonus” ebbed away, at least for men: By middle age, male college graduates raised in poverty were earning less than nondegree holders born into the middle class. The scholars conclude, “Individuals from poorer backgrounds may be encountering a glass ceiling that even a bachelor’s degree does not break.”

The authors don’t speculate as to why this is the case, but it seems that students from poor backgrounds have less access to very high-income jobs in technology, finance and other fields. Class and race surely play a role.

We appear to be approaching a time when, even for middle-class students, the economic benefit of a college degree will begin to dim. Since 2000, the growth in the wage gap between high school and college graduates has slowed to a halt; 25 percent of college graduates now earn no more than does the average high school graduate.

Part of the reason is oversupply. Technology increased the demand for educated workers, but that demand has been consistently outpaced by the number of people — urged on by everyone from teachers to presidents — prepared to meet it.