The Early Catastrophe: The 30 Million Word Gap by Age 3.

By age 3, children from privileged families have heard 30 million more words than children from underprivileged families. Longitudinal data on 42 families examined what accounted for enormous differences in rates of vocabulary growth. Children turned out to be like their parents in stature, activity level, vocabulary resources, and language and interaction styles. Follow-up data indicated that the 3-year-old measures of accomplishment predicted third grade school achievement.