Consistent with Biological Sensitivity to Context and Differential Susceptibility hypotheses, this study found that children who, as infants, were more temperamentally reactive were more sensitive to the quality of childcare they experienced as toddlers, but not to the amount of childcare with peers they had experienced since birth. Children with both highly positively and negatively reactive temperaments were more socially integrated when care quality was higher and less integrated when care quality was lower compared with moderately reactive children. Reactive temperament was not found to moderate relations between care quality or care duration and internalizing or externalizing behavior problems. These findings support the need to consider individual differences among children in evaluating the impacts of childcare. (Contains 3 tables and 1 figure.)