In the past quarter century, the nation’s K-12 public schools have experienced a large influx of students who speak languages other than English. Research has shown that many factors affect how English learner (EL) students acquire English language skills, including their preparation before entering U.S. schools, their out-of-school environments, and schools’ educational practices. High-quality afterschool programs offer many benefits, including academic achievement, but research has not focused specifically on the effects of afterschool programs on English language development. The literatures on both afterschool programming and English acquisition point to the potential importance of non-academic settings in helping EL students learn English. In this article, the authors use an innovative data source–the Youth Data Archive–to follow elementary and middle school students from a single school district over four academic years to discern any links between their afterschool program participation and English language development. The authors found that students attending the program had greater rates of gain in English development, but they did not necessarily achieve proficiency gains or redesignation as “fluent English proficient” sooner than non-participating students. The results point to the need for increased examination of the link between in-school and out-of-school activities in relation to English language acquisition.