Student mobility -- that is, students changing schools -- can be detrimental for the academic outcomes of mobile students. Students who change schools tend to experience lower test scores than their nonmobile peers, be at higher risk of getting retained a grade, and have higher drop-out rates. Student mobility may not only affect the academic achievement of the students who change schools, but also have implications for entire schools, especially when they are rated on student outcomes in state accountability systems. This brief examines school-year mobility rates and what they mean for schools, specifically: (1) were changes in school-year mobility rates associated with changes in school accountability performance?; and (2) how much did school-year mobility rates change from one year to the next at individual schools? To answer these research questions, Public Education Information Management Systems (PEIMS) data were used to identify school-year mobility and calculate a mobility rate for schools in 10 school districts around the Houston area. The study found that the higher the school-year mobility rate at a school, the lower its accountability performance. This association was largest in high schools, where school-year mobility rates fluctuated yearly, but was seen in elementary and middle schools as well. Implications for schools in the Houston area are discussed.