The part of the brain most affected by early stress is the prefrontal cortex, which is critical in self-regulatory activities of all kinds, both emotional and cognitive. As a result, children who grow up in stressful environments generally find it harder to concentrate, harder to sit still, harder to rebound from disappointments, and harder to follow directions. And that has a direct effect on their performance in school.

What matters most in a child’s development, they say, is not how much information we can stuff into her brain in the first few years. What matters, instead, is whether we are able to help her develop a very different set of qualities, a list that includes persistence, self-control, curiosity, conscientiousness, grit, and self-confidence. Economists refer to these as noncognitive skills, psychologists call them personality traits, and the rest of us sometimes think of them as character.

The part of the brain most affected by early stress is the prefrontal cortex, which is critical in self-regulatory activities of all kinds, both emotional and cognitive. As a result, children who grow up in stressful environments generally find it harder to concentrate, harder to sit still, harder to rebound from disappointments, and harder to follow directions. And that has a direct effect on their performance in school.

If we don't give kids the opportunity to fail when they're growing up, and to fail productively, to fail creatively, that they're going to get out there into the world and they're going to hit some kind of setback, like everybody does, and they're going to get completely derailed.

Optimists, by contrast, look for specific, limited, short-term explanations for bad events, and as a result, in the face of a setback, they’re more likely to pick themselves up and try again.

What if the Secret to Success is Failure?.

And in most highly academic environments in the United States, no one fails anything.