A heartbreaking social statistic is that children on welfare have only about half as many words per day directed at them as the children of working-class families- and less than one-third as many words as children whose parents are professionals. This is especially painful in view of the fact that scientists have found that the actual physical development of the brain is affected by how much interaction young children receive.

Even if every child entered the world with equal innate ability, by the time they were grown they would nevertheless have very different mental capabilities. Innate ability is the ability that exists at the moment of conception, but nobody applies for a job or for college admission at the moment of conception. Even between conception and birth, other influences affect the development of the brain, as well as the rest of the body.