For the monolingual population, research has shown that vocabulary knowledge is closely related to reading achievement. However, the role of vocabulary has not been studied as extensively in the bilingual population. It is important to look at vocabulary to better understand reading achievement in the bilingual population in the United States. This study investigated the predictors of Spanish and English vocabulary for 96 fifth-grade Latino English language learners. Our results suggest that becoming or staying proficient in English did not require parental use of English in the home. However, proficiency in Spanish required both instructional support at school and social support at home; it is likely that the low social status of Spanish is related to its greater dependence on home support.