- Dual Language Learners (DLLs) represent a substantial subpopulation in United States preschool programs (Aikens, Kinas, Malone, Tarullo, & Harding, 2017). DLLs often come from low socio-economic backgrounds and encounter barriers to academic success (National Academies of Science, 2017; Thomas & Collier, 2002). One consistent predictor of academic success is executive function (EF; McClelland, Acock, Piccinin, Rhea, & Stallings, 2013), which includes components such as inhibitory control, cognitive flexibility, and working memory (McClelland, Geldhof, Cameron, & Wanless, 2015; Ursache, Blair, & Raver, 2012). It is still unclear which EF components are related to second language proficiency in preschool. The present study examined relations between EF and English proficiency (as measured by the preLAS; Duncan & De Avila, 1998), utilizing four measures of EF as well as a composite EF variable. A total of 74 Spanish-speaking DLL children were assessed during fall and spring of the preschool year in either English or Spanish (depending on level of proficiency). Controlling for age and gender, results demonstrated that higher English proficiency in the fall predicted higher EF in fall via the working memory task (ß = .43, SE(ß) = .08, p < .0001). Higher English proficiency in spring predicted higher EF in spring via both the working memory task (ß = .29, SE(ß) = .14, p = .04), and the Head-Toes-Knees-Shoulders task (ß = .38, SE(ß) = .17, p = .02). Furthermore, regressions showed that increases in English proficiency from fall to spring predicted increases in spring EF on the HTKS task (ß = .33, z(7) = 2.64, p < .01) and the working memory task (ß = .42, z(7) = 3.45, p < .001), when controlling for fall EF and English proficiency variable. Results of this study inform both policy and practice related to instruction of DLL students, highlighting the need for EF interventions as well as equitable bilingual education programs in preschool- which research demonstrates are the most effective for long-term linguistic and academic success (National Academies of Science, 2017; Steele et al., 2017).