Prior research suggests that Spanish-speaking Dual Language Learners (DLLs)--young children who must master two languages simultaneously, their home language and English (Espinosa, 2013)--differentially benefit from quality Early Childhood Education (ECE), and in particular from Head Start, compared with children of other subgroups and monolingual-English children (Buysse, Peisner-Feinberg, Páez, Hammer, & Knowles, 2014; Gormley, 2008; Loeb, Bridges, Bassok, Fuller, & Rumberger, 2007; U.S. DHHS, 2010a). Despite the positive impacts of ECE for Spanish-speaking DLLs, however, the literature has not sufficiently investigated the mechanisms underlying this finding, or what may account for these differential benefits. The purpose of the current study is to determine whether Spanish language instruction is associated with school readiness skills for Head Start-eligible Spanish-speaking DLL children. It examines the relationship between Spanish instruction used by caregivers in Head Start settings and DLL children's subsequent English language academic achievement, as this may prove essential for their kindergarten readiness. Tables and figures are appended.