Children’s early experiences, either positive or negative, are cumulative in the sense that if an experience occurs occasionally, it may have minimal effects. If positive or negative experiences occur frequently, however, they can have powerful, lasting, even “snowballing,” effects. For example, a child’s social experiences with other children in the preschool years help him develop social skills and confidence that enable him to make friends in the early school years, and these experiences further enhance the child’s social competence. Conversely, children who fail to develop minimal social competence and are neglected or rejected by peers are at significant risk to drop out of school, become delinquent, and experience mental health problems in adulthood.