Using data from seven cohorts of language immersion lottery applicants in a large, urban school district, we estimate the causal effects of immersion on students’ test scores in reading, mathematics, and science, and on English learners’ (EL) reclassification. We estimate positive intent-to-treat (ITT) effects on reading performance in fifth and eighth grades, ranging from 13 to 22 percent of a standard deviation, reflecting 7 to 9 months of learning. We find little benefit in terms of mathematics and science performance, but also no detriment. By sixth and seventh grade, lottery winners’ probabilities of remaining classified as EL are three to four percentage points lower than those of their counterparts. This effect is stronger for ELs whose native language matches the partner language.