Using recent and nationally representative data from the Early Childhood Longitudinal Study-Birth Cohort, this study documents the substantial extent to which early childhood education program quality, defined using multiple measures, differs between (1) formal and informal providers; (2) Head Start, pre-kindergarten, and other centers and; (3) programs serving toddlers and those serving four-year olds. These large quality gaps are not explained by differential selection patterns into early childhood sectors by race and ethnicity or SES, and notably, differences in the quality of early education programs across demographic groups are much smaller than differences across sector. The observed quality differences are a likely mechanism for the well-documented differential effects of childcare settings on children's development. Implications for policy are discussed. (author abstract)