Abstract
Previous research indicates that exposure to nonparental child care at an earlier age and for more hours predicts, at the individual level, more aggressive and disobedient behavior and greater school preparedness. The present study extended child-care research by investigating classroom-composition effects, that is, effects of the combined child-care histories of all the children in the classroom. Analyses showed that effects at the individual level aggregate at the classroom level: Kindergarten children with limited or no child-care history exhibited more externalizing behavior (e.g., fighting and arguing) and higher academic achievement when schooled in classrooms with more peers who had extensive child-care histories.