Teachers in early childhood education (ECE) settings are central to providing children with high-quality experiences that promote both early development and long-term well-being; unfortunately, rates of teacher turnover are high in ECE settings. There are strong theoretical reasons to assume turnover is negatively linked with children's academic and socioemotional development, but few empirical studies test this hypothesis. Using an econometric fixed effects approach in two waves of data from the nationally representative Head Start Family and Child Experiences Survey, this study provides the first national estimate of the relationship between within-year lead teacher turnover and children's development in Head Start. I find an annual within-year turnover rate of [approximately]9%, about twice that of K-12, and that turnover is negatively associated with children's language outcomes alongside suggestive evidence for behavioral outcomes.