For some college graduates, their bachelor's degree will never be worth what they paid for it, a stark truth that contradicts the general assumption that college will bring a better life and a bigger paycheck, according to a national report released Wednesday.

While a college education, on average, results in greater lifetime earnings than those with less education make, that's not always the case. Where someone goes to college, what they study and how much they pay for a bachelor's degree makes a difference, according to the Brookings Institution report.

"College is a not a homogeneous thing, and a degree is not a uniform ticket," said Isabel Sawhill, senior fellow at Brookings, a national policy think tank. "There are lots of different types of tickets, and some of those tickets take you nowhere."

For example, those attending less competitive colleges or universities are less likely to finish a degree and, if they do, still make less money than those from a selective college, according to the report, co-authored by Sawhill and Stephanie Owen, Brookings senior research assistant.

In addition, public colleges typically offer a better return on the investment than private ones.

The authors also point out that less than 60 percent of students who enter a four-year college finish within six years. And the 40 percent who do often leave with significant debt.

College-prep emphasis

"For certain schools, majors, occupations and individuals, college may not be a smart investment," the authors said. "By telling all young people that they should go to college no matter what, we are actually doing some of them a disservice."

Yet in high schools and homes across the country, a higher-education degree is considered a must. President Obama, in his 2012 State of the Union, called college an "economic imperative."

Locally, school districts across the Bay Area, including San Francisco and Oakland, have recently adopted policies requiring all high school graduates to complete a college-prep sequence of courses.

"Our focus in SFUSD is to make sure students have options when they graduate from high school," said San Francisco Unified spokeswoman Gentle Blythe. "We're committed to our graduates' being equipped with the knowledge and skills that will help them make a successful transition into a fulfilling career, which may include college, vocational school or going directly into the workforce."

Still the overall message kids hear is: "College, college, college," Sawhill said.

Less value

But a degree doesn't buy what it did in years past - a signal that "they have entered into this magic circle," Sawhill said. "The more people who get into the circle, the less value it has."

About 30 percent of adults over age 25 had a bachelor's degree in 2010, up from 26 percent 10 years earlier, according to census data.

As enrollment has grown, so has debt. Federal student loans now total nearly $1 trillion, more than credit card or auto loan debt, according to the study.

Students take on the debt believing they are buying a future that may not become reality, and an increasing number are defaulting on their loans, according to national credit agencies.

Those with a degree will make, on average, $570,000 more over a lifetime than a high school graduate.

Negative returns

Yet at least 200 colleges across the country show a negative return on investment when considering the cost of attending versus lifetime career earnings, according to the researchers.

And majors matter, with engineering, math, technology and science a better bet than, say, art or education, which are among the majors offering the lowest return on investment.

The authors acknowledged that getting a degree and choosing a career isn't always about making big bucks.

But families and students should know what they're likely to get later in life when they walk into a particular hall of academia.

The policy brief calls for helping parents understand more detailed information about colleges, including the availability of financial aid and completion rates.

The authors also recommended simplifying the financial aid system so it's not so overwhelming to families, while also tying federal grants to student performance to boost completion rates.

Alternatives

And finally, they recommended that high schools encourage alternatives to college, including vocational programs and apprenticeships, focusing on high-demand occupations for those who don't opt for academia after high school.

"All of this suggests that it is a mistake to unilaterally tell young Americans that going to college - any college - is the best decision they can make," according to the report. It added: "If they choose wisely and attend a school with generous financial aid and high expected earnings, and if they don't just enroll but graduate, they can greatly improve their lifetime prospects."

Jill Tucker is a San Francisco Chronicle staff writer. E-mail: jtucker@sfchronicle.com