This article analyzes the role that individual differences in children's cognitive, Spanish competence, and socio-emotional and behavioral skills play in predicting the concurrent and longitudinal acquisition of English among a large sample of ethnically diverse, low-income, Hispanic preschool children. Participants assessed at age 4 for language, cognitive, socio-emotional, and behavioral skills were followed through kindergarten. Multivariate analyses demonstrated that Spanish-speaking preschoolers with greater initiative, self-control, and attachment and fewer behavior problems at age 4 were more successful in obtaining English proficiency by the end of kindergarten compared to those initially weaker in these skills, even after controlling for cognitive/language skills and demographic variables. Also, greater facility in Spanish at age 4 predicted the attainment of English proficiency. Social and behavioral skills and proficiency in Spanish are valuable resources for low-income English language learners during their transition to school. (author abstract)