In this study, we evaluate the efficacy of teacher communication with parents and students as a means of increasing student engagement. We estimate the causal effect of teacher communication by conducting a randomized field experiment in which sixth- and ninth-grade students were assigned to receive a daily phone call home and a text/written message during a mandatory summer school program. We find that frequent teacher-family communication immediately increased student engagement as measured by homework completion rates, on-task behavior, and class participation. On average, teacher-family communication increased the odds that students completed their homework by 40%, decreased instances in which teachers had to redirect students' attention to the task at hand by 25%, and increased class participation rates by 15%. Drawing upon surveys and interviews with participating teachers and students, we identify three primary mechanisms through which communication likely affected engagement: stronger teacher-student relationships, expanded parental involvement, and increased student motivation.