PARIS — NOT many Ivy League professors are associated with a type of candy. But Walter Mischel, a professor of psychology at Columbia, doesn’t mind being one of them.

“I’m the marshmallow man,” he says, with a modest shrug.

I’m with Mr. Mischel (pronounced me-SHELL) in his tiny home office in Paris, where he spends the summer with his girlfriend. We’re watching grainy video footage of preschoolers taking the “marshmallow test,” the legendary experiment on self-control that he invented nearly 50 years ago. In the video, a succession of 5-year-olds sit at a table with cookies on it (the kids could pick their own treats). If they resist eating anything for 15 minutes, they get two cookies; otherwise they just get one.

I’ve given a version of the test to my own kids; many of my friends have given it to theirs. Who wouldn’t? Famously, preschoolers who waited longest for the marshmallow went on to have higher SAT scores than the ones who couldn’t wait. In later years they were thinner, earned more advanced degrees, used less cocaine, and coped better with stress. As these first marshmallow kids now enter their 50s, Mr. Mischel and colleagues are investigating whether the good delayers are richer, too.

At age 84, Mr. Mischel is about to publish his first nonacademic book, “The Marshmallow Test: Mastering Self-Control.” He says we anxious parents timing our kids in front of treats are missing a key finding of willpower research: Whether you eat the marshmallow at age 5 isn’t your destiny. Self-control can be taught. Grown-ups can use it to tackle the burning issues of modern middle-class life: how to go to bed earlier, not check email obsessively, stop yelling at our children and spouses, and eat less bread. Poor kids need self-control skills if they’re going to catch up at school.