Earlier acquisition of English is associated with better academic performance for dual language learners (DLLs), but large-scale, prospective, longitudinal studies examining how trajectories for English acquisition relate to school-based outcomes, accounting for relevant covariates, are rare. We explored how the grade in which DLLs (N = 17,548; 47% female; 80% free/reduced-price lunch; 86% Latino, 10% Black, and 4% White/Other) acquire English proficiency, defined by the school district, relates to academic outcomes (grade retention, GPA, reading and math test scores) in 5th grade, controlling for gender, ethnicity, poverty, and school readiness skills at age 4. Earlier acquisition of English, especially before 2nd grade, predicted better performance on each 5th grade outcome. Earlier proficiency in English was even more important for 5th grade outcomes for those with initially high cognitive skills, Latino/Hispanic DLLs (compared to Black DLLs), and those not in poverty. Implications for practice and research are discussed.