Stressful family experiences. Factors that predict reduced intellectual competence include, among others, having a father who does not live with the family, a mother with a history of mental illness, parents with limited work skills, and a history of stressful events, such as domestic violence, early in life (Sameroff et al., 1987). On average, each risk factor reduces a child’s IQ score by 4 points. And when children live in severely disadvantaged neighborhoods, their IQs decline over time, even after they have moved to better areas; the drop is comparable to that seen when a child misses a year of school
