When parents praise their children’s intelligence, they believe they are providing the solution to this problem. According to a survey conducted by Columbia University, 85 percent of American parents think it’s important to tell their kids that they’re smart. In and around the New York area, according to my own (admittedly nonscientific) poll, the number is more like 100 percent. Everyone does it, habitually. The constant praise is meant to be an angel on the shoulder, ensuring that children do not sell their talents short.

But a growing body of research—and a new study from the trenches of the New York public-school system—strongly suggests it might be the other way around. Giving kids the label of “smart” does not prevent them from underperforming. It might actually be causing it.

For the past ten years, psychologist Carol Dweck and her team at Columbia (she’s now at Stanford) studied the effect of praise on students in a dozen New York schools. Her seminal work—a series of experiments on 400 fifth-graders—paints the picture most clearly.

It didn’t take long. The teachers—who hadn’t known which students had been assigned to which workshop—could pick out the students who had been taught that intelligence can be developed. They improved their study habits and grades. In a single semester, Blackwell reversed the students’ longtime trend of decreasing math grades.

The only difference between the control group and the test group were two lessons, a total of 50 minutes spent teaching not math but a single idea: that the brain is a muscle. Giving it a harder workout makes you smarter. That alone improved their math scores.

“These are very persuasive findings,” says Columbia’s Dr. Geraldine Downey, a specialist in children’s sensitivity to rejection. “They show how you can take a specific theory and develop a curriculum that works.” Downey’s comment is typical of what other scholars in the field are saying. Dr. Mahzarin Banaji, a Harvard social psychologist who is an expert in stereotyping, told me, “Carol Dweck is a flat-out genius. I hope the work is taken seriously. It scares people when they see these results.”

How do you give the brain a harder workout?

working at problems above your current knowledge base?

But it has to be close to what you already know, otherwise you'll be lost.

perhaps for only a time? 

It's a progression. What you work on next needs to build on what you already know so that it's challenging but still achievable.