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). This research brief uses Texas Public Education Information Management System (PEIMS) six week attendance records data from the 2010-11 through 2016-17 school years to describe these three pieces of school year mobility: mobility entering a school, mobility departing a school, and net mobility. Each type of mobility is presented as a count (i.e., number of school changes) and as a rate (i.e., number of moves per 100 students). 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. [For "Changing Schools, Part 1: Student Mobility during the Summer Months in Texas and the Houston Area," see ED611142.]