The Intensity of Formal Child-Care Attendance Decreases the Shared Environment Contribution to School Readiness: A Twin Study.

The purpose of this study was to explore if child-care intensity (hours/weeks) and age of onset could moderate genetic and environmental contributions to school readiness. A sample of 648 (85% Whites; 50% Females) pairs of twins was used to compute a GxE, CxE and ExE interaction analyses. The moderation model showed that shared environment explains 48% of individual differences in school readiness for children not attending formal child-care, and decreased gradually to a mere 3% for children attending formal child-care full time, e.g., 40 h per week. Age of onset exerted no moderation effect. The results support the hypothesis that child-care acts as a normalizing environment, possibly buffering negative effects from low-quality home environments on school readiness.