School attendance is strongly associated with academic success and high school completion, but approximately one-in-seven students miss nearly one month of school each year. To address absenteeism, we partnered with four public school districts in the metro-Atlanta area and experimentally deployed email and text messages to inform parents about their child's attendance. Parents received personalized monthly messages through the school districts' existing messaging platforms that had zero marginal cost per message. The messages informed parents about their child's number of absences and how that number compared to absences of their peers. For most parents, this information was delivered through email as opposed to text, and parents of students most in need of improved attendance were the hardest to reach. Intent-to-treat estimates show the intervention reduced end-of-year absences by four-tenths to two-thirds of a day (2 to 3%) and reduced the probability of chronic absenteeism by 2 to 6%, while actually receiving the messages reduced end-of-year absences by two-thirds to almost one day (3 to 4%) and reduced the probability of chronic absenteeism by 4 to 7%. [This is the online first version of an article published in "Journal of Research on Educational Effectiveness."]