While current debates center on whether and how to admit immigrants to the United States, little attention has been paid to interventions designed to help immigrants integrate after they arrive. Public adult education programs are the primary policy lever for building the language skills of the over 23 million adults with limited English proficiency in the United States. We leverage the enrollment lottery of a publicly-funded adult English for Speakers of Other Languages (ESOL) program in Massachusetts to estimate the effects of English language training on voting behavior and employer-reported earnings. Attending ESOL classes more than doubles rates of voter registration and increases annual earnings by $2,400 (56%). We estimate that increased tax revenue from earnings gains fully pay for program costs over time, generating a 6% annual return for taxpayers. Our results demonstrate the social value of post-migration investments in the human capital of adult immigrants.