Researchers are finding that poverty can harm the brains of small children, perhaps because their brains are subjected to excessive cortisol (a stress hormone) and exposed less to conversation and reading. One study just published in Nature Neuroscience found that children in low-income families had a brain surface area on average 6 percent smaller than that of children in high-income families.  "Neuroscience tells us we're missing a critical, time-sensitive opportunity to help the most disadvantaged kids," notes Dr. Jack Shonkoff, an early childhood expert at the Harvard Graduate School of Education.

Growing evidence suggests what does work to break the poverty cycle: Start early in life, and coach parents to stimulate their children. Randomized controlled trials, the gold standard of evidence, have shown this with programs like Nurse-Family Partnership, Reach Out and Read, and high-quality preschool. These kinds of interventions typically produce cognitive gains that last a few years and then fade - but, more important, alsoproduce better life outcomes, such as less crime, fewer teenage pregnancies, higher high school graduation rates, and higher incomes.