Young Spanish-speaking Latinos in the U.S., most of whom are from low-income backgrounds, perform below their English-speaking peers at kindergarten entry. This achievement gap is concerning considering the rising number of Latino children in the U.S. living in poverty. Despite this risk, a large body of research highlights the positive effects of learning two languages. Latino DLLs attending Head Start, compared to their monolingual peers, were recently found to have higher executive functioning (EF), a set of domain-general cognitive skills that robustly predict academic achievement. This emerging evidence is encouraging, however, there is still a lack of research on how this bilingual-EF advantage contributes to young DLLs' school readiness in the context of early education classrooms. To better understand these factors, this study examined bilingual language, EF, and science achievement across the year in a sample of 424 Latino preschool DLLs across 38 Head Start classrooms. Children were assessed in the fall and spring on all measures, and observations of Spanish and English support in the classroom were conducted in the winter. Results from a cross-lag model demonstrated a significant bidirectional relationship between bilingual ability and EF across the year, and also indicated positive effects of both constructs on children's science at the end of the year. Spanish and English support in the classroom did not influence the cross-lag paths between bilingual ability and EF across the year, however, English support appeared to moderate children's EF from fall to spring, and Spanish support predicted both bilingual ability and EF at the end of the year. Results from this study help inform the mechanisms behind the bilingual-EF relationship and demonstrate positive effects on achievement. Additionally, findings highlight the importance of supporting English and Spanish. Additionally, findings highlight the importance of supporting English and Spanish for DLLs in the early childhood classroom. (author abstract)