Social-emotional adjustment in early childhood has been associated with later social development and academic achievement. Language proficiency is a central tool for building social relationships and managing emotions. Limited English proficiency in early childhood may pose challenges for children's social-emotional development. This study used secondary data from the Head Start Impact Study to examine the influence of English proficiency on ELL children's internalizing and externalizing behaviors during preschool. In addition, this study examined the roles of parent involvement and teacher-child relationships in predicting ELL children's social-emotional adjustment. 295 ELLs and 935 non-ELLs were selected to analyze for this study. (author abstract)