We examine the relationship between early cognitive development, socioeconomic status (SES), child health, and parenting quality in a developing country. We use a sample of more than 3,000 predominantly poor preschool-aged children from Ecuador, and analyze determinants of their scores on a widely used test of language ability. We find that household wealth and parental education are associated with higher scores, and that these associations are larger among older children. Child health and measures of parenting quality are associated with test performance, and account for a fraction, although not the majority, of the association between SES and cognitive development. (Contains 8 tables, 5 figures and 26 footnotes.)