This study investigates the reliability and validity of the Child Care Ecology Inventory (CCEI), a measure of the quality of family child care in the social domain. The CCEI focuses on research-based environmental features and caregiving practices for promoting positive social development in preschool-age children. A total of 198 family child care homes in the Northwest USA participated. Good scale reliabilities were found for the measures of the environment (Enrichment and Organization) and for caregivers' practices (Monitoring, Positive Attention, Promoting Social Skills, and Teaching Rules) and interrater reliability was adequate for research purposes. The CCEI was associated with other commonly used measures of child care quality that assessed similar environmental and caregiving constructs. Linear regression models were run to determine the features of family child care quality that were concurrently associated with observed child behavior. The child-caregiver ratio, Environment Organization, and caregivers' Teaching Rules were negatively associated with children's problem behavior (noncompliance and aggression). Caregivers' provision of Planned Activities/Routines and Positive Attention were associated with positive child behavior. Results indicate that different aspects of quality are related to different aspects of children's social interactions and behaviors. (author abstract)