Tens of thousands of students in the Houston area switched schools during the school year annually. In moving from one school to another, students often experienced disruptions to their education. This study examined what this mobility meant for students' performance on state accountability tests, high school grade retention, high school dropout, and high school graduation. In the state of Texas, students who changed schools during the school year saw a decline in their State of Texas Assessments of Academic Readiness (STAAR) scores. Student mobility also increased the chances a student was retained during their freshman year of high school. Finally, students who changed schools were at a higher risk of dropping out of high school and were less likely to graduate on-time (i.e., within four years).