Graduating on time makes college a better investment. (AP Photo/Jessica Hill)

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.”

College is still worth it for the average student. But Benson’s study found returns are particularly modest for young men at the CSU system, mostly because of high dropout rates, delayed graduation and a lower effect on labor force participation compared with women.

“The return to a college degree in 2010,” researchers wrote, “could be less than the interest on unsubsidized Stafford loans.”

More students than ever are going to college. But the nation’s overall college graduation rate has stayed low. (Check out this Jeff Guo piece about the heart-breaking forces driving this problem.)

In 2013, 65.9 percent of graduating high school seniors enrolled in a two- or four-year college, a level Benson noted is “only modestly” above the percentage in the early 90s. Weak enrollment could be a symptom of college sliding down on the public’s Worth It scale.

Those who do graduate are taking longer and longer to earn diplomas: Less than 60 percent of full-time students who are enrolled in college for the first time graduate within six years, according to the Institute of Education Sciences. (Part-time, older, low-income and minority students tend to have an even lower completion rate.)

It’s not surprising that the study finds students who take out loans and don’t graduate on time incur much more debt. Two extra years on campus increases the balance by nearly 70 percent, according to data from Temple University and the University of Texas, Austin.

Benson’s team saw students in the more selective UC system, which spends twice per student as the less prestigious CSU system, graduate more quickly: 80 percent of entering freshmen finish a degree within six years.

But out of the 34,000 freshmen who entered the CSU system in 1997, only 35.3 percent earned a degree in four years and 62.8 percent earned a degree within 12 years. The researchers partially blame “enrollments that increase faster than spending making it harder to enroll in required classes, harder to get academic help, and so on.”

On top of this, UC graduates earned an average of 10 percent more income after graduation, according to data researchers analyzed from payscale.com. The higher pay — and higher chance you’d graduate in a timely fashion — offset the higher tuition in scenarios where graduates scored jobs in lucrative fields.

Nationally, the pay gap between college graduates and people lacking degrees recently reached a record high, according to Labor Department statistics analyzed by the Economic Policy Institute. Americans with four-year college degrees made 98 percent more per hour on average in 2013 than people without diplomas, up from 89 percent five years earlier and 85 percent a decade earlier. This gap is growing, in large part, because wages for non-college grads are shrinking faster wages for college grads.

Benson’s conclusion: The investment of a college education is generally better for those who graduate — and on time — from a school with healthier resources.

“Students have some control over if they graduate and when,” Benson said, so, knowing this, America’s youth is better equipped to weigh the risks before making educational plans after high school.