Why college isn’t always worth it. A new study suggests the economic return on a college degree may be a lot more modest than you think.

The Washington Post reports:

Earlier this month, after announcing his plan to make community college free, President Obama lauded a college degree as "the surest ticket to the middle class."

New research in the prolific field of “Is College Worth It?” suggests it’s not that simple.

“‘Ticket’ implies a college degree is something you can just cash in,” said Alan Benson, assistant business professor at the University of Minnesota. “But it doesn’t work that way. A college degree is more of a stepping stone, one ingredient to consider when you’re cooking up your career. … It’s not always the best investment for everyone.”

Benson, along with M.I.T.’s Frank Levy and business analyst Raimundo Esteva, co-authored a new paper, released this week, examining the value of public university options in California. Factors like how long it takes to complete a degree — often longer than four years — and whether students make it to graduation, he learned, can significantly diminish the value of pursuing higher education.

Data from the Census Bureau, the University of California system and the less selective California State University system revealed a gap in the economic return between the schools. Similar disparities persist nationwide, Benson said, exacerbated by scarcer resources at second-tier institutions.

For some students, the gap can make college a risky investment. It’s no longer a sure thing that graduation happens on time.

“Applying more realistic assumptions,” the researchers wrote, “we show that many students — particularly young men who cannot access top-tier universities — face an economic return to college that, while positive on average, can reasonably inspire caution among student and their parents.”

The law of diminishing returns applies ... even to higher education.