The current study examined the social and language development of 345 Spanish-speaking pre-kindergartners who attended pre-kindergarten programs that varied widely in how much Spanish was spoken in the classroom by the teacher. Previous studies on English language learners have focused on how the language of instruction impacts children's language proficiency, ignoring the context in which children are learning. The current study found better social skills and closer teacher-child relationships in classrooms where teachers spoke some Spanish. Teacher ratings of children's peer social skills and assertiveness were positively associated with increased amounts of Spanish being spoken. More Spanish language use in the classroom was also related to a decrease in children's likelihood of being victims of aggression as rated by independent observers. The findings have implications for better understanding how policy decisions regarding language of instruction impact children in the social domain. As early education programs are faced with the challenging task of developing best practices for English language learners, it is essential that programs are attentive to the social implications of language.