Student mobility refers to students changing schools. In this series of research briefs, the Houston Education Research Consortium (HERC) examines and describes the amount of student mobility in Texas, with particular focus on Houston area public schools. This second research brief focuses on providing an overview of how much mobility takes place during the school year (i.e., within school years). Other research briefs give more detail on school changes during the summer time, the percentage of mobility that stays within district and how much crosses between school districts, as well as differences in mobility across subgroups of students.