The college years can be a time for experimentation and self-discovery, and a degree can improve your potential income by more than $20,000 annually. However, over the past 20 years, more than 31 million Americans, almost 10 percent of the current population, left their college education uncompleted, according to a new report from the National Student Clearinghouse. 

Even though the U.S. higher education system has been ranked as the best in the world, politicians and advocates say it is in need of improvement. For years, the U.S. led the globe in the highest percentage of college graduates. But in the past decade, it has fallen from the top of the rankings, most recently coming in in 16th place.

In 2010, President Barack Obama announced an initiative to increase the percentage of Americans with college degrees to 60 percent by 2020. But while the number of degree holders has increased, experts predict that at the current rate it may not be enough for a robust workforce.

Tapping into the group of Americans who opened the door to a degree but never walked through may be essential to achieving the national goal for higher education and closing the gap for skilled workers. 

In deciphering why so many have left college unfinished, the researchers highlighted 10 million who attended college for only one semester and around 18 million who spent years attending school but never graduated or accumulated at least two years' worth of credits. After acknowleding other potential factors like cost, they hypothozized that many of these students were inadequately prepared for college. While high schools typically train students for what they might expect in college, the numbers suggest more preparation is needed.

The researchers also identified how difficult it is to follow an unconventional path through college, like attending multiple schools or enrolling as an adult. Statistically, the more institutions they attented and they older they were, the less likely they were to complete their education.

By improving preparation for higher education in public schools and starting programs to help students transfer credits and adapt to the college enviroment, institutions and policymakers could help students stay in school until graduation.

The report also identified that there are almost 4 million former students who finished more than two years of classes but never completed their degrees.

And while efforts traditionally center on attracting graduating high school students, reaching out to unconventional markets may be the key to putting degrees in the hands of more Americans.