Using a nationally representative sample of 3- and 4-year-old Spanish-speaking dual language learners (DLLs) attending Head Start (N = 654), this study examined whether mean levels of and variability in peers' English receptive vocabulary skills were associated with DLLs' English and Spanish receptive vocabulary skills in the spring. In addition, I tested whether these associations differed depending on the proportion of DLLs in the class. Results showed that DLLs had better English receptive vocabulary growth, but weaker Spanish receptive vocabulary growth when their classmates had higher English receptive vocabulary skills. Variability in peers' English receptive vocabulary skills was not significantly associated with vocabulary growth in English or Spanish. These patterns did not depend on the proportion of DLLs in the class, pointing to the utility of understanding peer effects in terms of classmates' skills and not only their characteristics. Findings demonstrate the importance of classmates' English vocabulary skills for English vocabulary development. However, additional supports are needed to maintain DLLs' vocabulary development in Spanish.