It’s that time of year; high school seniors are starting to think about colleges and where to go, but if you’re having doubts, it’s worth considering that some of America’s most powerful CEO’s never even made it through the doors of an academic institution after high-school, and others who did, dropped out midway.

The one thing these “college dropouts” all have in common is that they started work young and haven’t stopped since.

For more on career advice, watch this video:

Todd Jones, Publix

Todd Jones, 54, might not have an official college degree but he’s a full-fledged graduate of the “University of Publix (PUSH)”. He spent four decades climbing the ranks of the supermarket chain before becoming CEO in January 2016. By this point, the former store clerk had tried his hand at almost every side of the business and now knows it better than anyone else.

Richard A. Gonzalez, AbbVie

Despite never graduating from college (and previously claiming that he did in his company bio), Richard Gonzalez, 61, has managed to keep a handle on AbbVie (ABBV)’s 28,000 employees and $23 billion annual revenue. Not your typical college dropout, Gonzalez quit school to make a start on his 30-year career in pharmaceuticals. He has run two global companies and already returned from retirement once; the quiet life just wasn’t for him.

John P. Mackey, Whole Foods Market

The so-called conscious capitalist clocked over 100 credits of college classes but never graduated. He was too preoccupied with an organic food store that he set up with then-girlfriend Renee Lawson Hardy to finish a degree. Perseverance and intuition paid off as it’s now the largest organic supermarket chain in the U.S. and goes by the name of Whole Foods (WFMC). But Mackey, 62, still lives up to his “free love” student years and only pays himself an annual salary of $1.

Sheldon Adelson, Las Vegas Sands

U.S. business magnate Sheldon Adelson, 82, hasn’t had the time or the necessity to complete a college degree. He kicked off his career at the tender age of 12 selling newspapers in Boston and has been hustling ever since. His willingness to experiment led him to set up a string of successful companies, including Las Vegas Sands (LVS), a sprawling casino empire, which stretches beyond the U.S. desert and across Asia. In recent years, Adelson has become a household name for his abundant funding of Republican candidates and causes.

Robert W. Pittman, iHeartMedia

“Bob” Pittman, 62, is a pioneer of modern American television. He was part of the team that created MTV and went on to run the network. Pittman was later chief operating officer of AOL during the company’s tie-up with Time Warner (TWX), widely considered one of the worst mergers of all time. Nonetheless, he managed to come out the other side unscathed, and now runs iHeartMedia, the largest broadcaster in the U.S. He doesn’t have a college degree to thank for his success but determination and hard work, which goes right back to the 15-year-old boy who started out in a radio studio in Mississippi.

John P. Tague, Hertz Global Holdings

John Tague, 54, learned everything on the job. He worked his way up to the top at United Airlines and pulled the company out of dark times by boosting sales in the early 2000’s. He was called into Hertz (HTZ) in late 2015 to run the company’s car rental business and their hoping he’ll do just the same. His ability to master any trade is the key to his success. Something he learned from his father at the kitchen table, not in college, he says.

Larry D. Young, Dr. Pepper

Larry Young, 61, has been in the soft drink industry for all of his working life, though in less glamorous seats than the CEO’s chair. He started out driving Pepsi (PEP) trucks and 40 years later is now responsible for more than 50 beverage brands. Young says he picked up everything on the road—not in class.