" But that doesn’t mean it’s impossible to shift a person’s motivation. In the short term, in fact, it can be surprisingly easy. Let’s stay in the candy aisle for a bit longer and consider a couple of experiments done decades ago involving IQ and M&M’s. In the first test, conducted in northern California in the late 1960s, a researcher named Calvin Edlund selected seventy-nine children between the ages of five and seven, all from “low-middle class and lower-class homes.” The children were randomly divided into an experimental group and a control group. First, they all took a standard version of the Stanford-Binet IQ test. Seven weeks later, they took a similar test, but this time the kids in the experimental group were given one M&M for each correct answer. On the first test, the two groups were evenly matched on IQ. On the second test, the IQ of the M&M group went up an average of twelve points—a huge leap. "

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