A college education may not be worth as much as you think.

For years, higher education was touted as a safe path to professional and financial success. Easy money, in the form of student loans, flowed to help parents and students finance degrees, with the implication that in the long run, a bachelor's degree was a good bet. Graduates, it has long been argued, would be able to build solid careers that would earn them far more than their high-school educated counterparts.

The...