We present results of a randomized control trial of a two-generation English as a Second Language (ESL) program in which all families participated in Head Start while treatment parents also enrolled in a high dosage, family-focused ESL curriculum with supportive services. Examining 197 parent-child dyads among Spanish- (89%) and Zomi-speaking (11%) immigrant families, we found improvements in participant parents' English reading skills and engagement with their child's teacher after one year. Parents with low levels of English proficiency (57%) at program start reported more positive parenting skills and lower levels of psychological distress whereas parents with more advanced English proficiency (43%) reported more parenting stress and higher levels of psychological distress. We did not find main effects on children's language and cognitive skills. We conclude by discussing policy implications of a two-generation approach for immigrant families.