And that's considered a good number. "Rates below 50 percent, 40 percent and even 30 percent are distressingly easy to find," USA Today reports of a study issued by the American Enterprise Institute, a conservative think tank. The study is based on data reported to the U.S. Department of Education by nearly 1,400 schools about full-time, first-time students who entered in fall 2001.

Harvard University, not surprisingly, has one of the highest graduation rates at 97 percent, while Southern University at New Orleans, which was slammed by Hurricane Katrina in 2005, reported 8 percent. Those are the extremes.

Often, schools that have comparable admissions standards have wildly different graduation rates, which indicates that some colleges are more effective in educating its students. When similar types of colleges have such large differences in their graduation rates, the report says, "It is fair to ask why."

For example, Walla Walla University and Heritage University, both of which are located in Washington state, are similar in that they each only require a high school diploma for admission. Yet Walla Walla reported a graduation rate of 53 percent, compared to Heritage's meager 17 percent.

Even colleges that attract the brightest students have similar stories. John Carroll University in Cleveland and Chicago State University in Illinois both require high school grades that average a B-minus or better, but John Carroll's graduation rate is 74 percent, vs. Chicago State's graduation rate of 16 percent. Among the most competitive schools, there is also a difference. Amherst College in Massachusetts and Reed College in Portland, Oregon, graduated 96 percent vs. 76 percent, respectively.

"While student motivation, finances and ability matter greatly when it comes to college completion, the practices of higher education institutions matter, too," lead author Frederick Hess told USA Today.

Graduation rates are so important that prospective students and their parents should consider this when choosing a college. "It's one of these little secrets that everybody in the industry knows," co-author Mark Schneider told USA Today. "We're just trying to highlight it."