This study examined the role of Spanish cognates in the English vocabulary development of bilingual Spanish speaking kindergarteners, adding to a growing body of research in the fields of psycholinguistics and education. Students in a transitional bilingual kindergarten class (n=21) were taught English and Spanish vocabulary words in a research based vocabulary curriculum. Evidence was found suggesting a cognate facilitation effect in word learning. Specifically, students who learned the Spanish target vocabulary words were 1.5 times more likely to learn the English cognate paired words than non-cognate translation pairs. Furthermore, these kindergarten students demonstrated the ability to infer the meaning of English cognate words that they had been taught only in Spanish. Findings from this study align with evidence in psycholinguistic studies showing a cognate facilitation effect in L2 word learning that makes cognates easier to learn and remember than non-cognate translations, and finds this evidence in an applied classroom setting. Collectively, the results of this study have implications for designing instruction that uses cognates to accelerate vocabulary development of ELLs.