A student relaxing outside the student center at St. Louis Community College at Meramec. Jerry Naunheim, Jr./Post-Dispatch

Natalia Kolesnikova, an economist for Federal Reserve Bank of St. Louis, last week published a study showing that for students interested in a “a route of upward economic mobility” community colleges are an incredible bargain.

That’s not news to most graduates of the two-year programs at community colleges in St. Louis or to employers who have hired them. Once regarded as the poor relatives of four-year colleges and universities, community colleges have improved steadily over the years. As costs of higher education have escalated, affordable education available at community colleges has become an even bigger bargain. That should worry, and maybe even light a fire under, the four-year colleges.

The St. Louis Fed study confirmed that community college campuses are more racially diverse, on average, than their four-year counterparts. They are home to more first-generation college students and attract a greater concentration of older students — 35 percent of their students are 30 or older.

Community college attendance brings long-term economic benefits. Workers with an associate’s degree earn more than their peers with a high school diploma; minority students experience the greatest gains.

In St. Louis, black men with an associate’s degree earn on average 13 percent more, while the return for black women is a stunning 43 percent increase — a fact the investigator attributes to a high concentration in nursing and other health care training.

The national media focused on a “dog bites man” aspect of the study — an unexplained statistical anomaly referred to as the “community college penalty.” Students who obtain a two-year associate’s degree and continue on to earn a bachelor’s or advanced degree at a four-year school earn less per year on average than peers who started at a four-year institution.

Ms. Kolesnikova said there there aren’t enough data to explain this discrepancy, but speculates it could be because community college students often come from poorly performing elementary and secondary schools. She said that’s a disadvantage that “affects their educational and labor market outcomes throughout their career.”

Still, community colleges deserve credit for putting “disadvantaged” students on a positive track — even though it may not yet have resulted in full wage-earning parity. And there’s reason to think the “penalty” will diminish as community college campuses attract a growing share of the nation’s best prepared and highest-achieving students.

Unlike many four-year schools, community colleges are not in a figurative arms race to build the flashiest student center or recruit celebrity faculty members. They focus on the basics. And one key basic is tuition cost.

The average community college costs in Illinois are 28 percent of those at the state’s four-year public institutions and 11 percent of private four-year colleges and universities. In Missouri, community college tuition and fees are 36 percent of what public colleges and universities charge, and 14 percent of the costs at private colleges and universities.

Community colleges already enroll 46 percent of the nation’s undergraduate students, according to the Fed study. As long as community colleges stay focused on fundamentals and keep costs affordable, those numbers will grow.