" Stress physiologists have found a biological explanation for this phenomenon as well. 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. When you’re overwhelmed by uncontrollable impulses and distracted by negative feelings, it’s hard to learn the alphabet. And in fact, when kindergarten teachers are surveyed about their students, they say that the biggest problem they face is not children who don’t know their letters and numbers; it is kids who don’t know how to manage their tempers or calm themselves down after a provocation. "

― Paul Tough , How Children Succeed: Grit, Curiosity, and the Hidden Power of Character