In response to high levels of student mobility between schools (GAO, 2010) and stresses to family residential stability brought on by the 2008 housing crisis, policy makers are increasingly aware of the need to address the impacts of student mobility on mobile students and their peers. Of the different types of mobility, mid-year entry and exit that occur after the school year begins are likely to be particularly disruptive and also to have important policy implications for schools and students. For example, schools with net increases in student enrollment between the fall and spring educate more students than they receive funding for, as per-pupil funding is largely determined by fall attendance. This means mid-year entrants may spread resources across greater numbers of students, forcing schools to operate with lower per-pupil funding and drawing resources away from stable students.

Most studies of student mobility examine the impact of mobility on the students who make the moves and conclude that moving negatively impacts academic achievement. Our own prior research shows that while different types of moves affect mobile students differently, mid-year moves negatively affect student achievement. In addition to affecting student movers, though, student turnover may also affect stable students. For example, stable students could be negatively affected by disruptions in the learning environment, and the changing composition of the student body could have positive or negative impacts on stable students depending on whether the new entrants are of higher or lower quality than existing peers.

In this study, we estimate the impact of mid-year entrants on stable students using data on New York City elementary and middle schools from 2005-2008.  Our core model links the performance of stable students to measures capturing the degree of mid-year entry and the characteristics of students entering in the middle of the school year. A full complement of school, grade, year, and student fixed effects means that the impact of mid-year entry is identified off of variation around the school-grade-year mean, which we argue is credibly viewed as random.  Thus, we use  “unexpected” variation in mobility to estimate the impact of mid-year entrants on the performance of stable classmates in the destination school. To examine potential compositional changes in the student body that result from mid-year mobility, we compare the characteristics of mid-year entrants to the stable students and mid-year exiters in their school-grade.

By comprehensively examining the impact of mid-year entrants on stable students, we are able to identify different impacts based on the characteristics of mid-year entrants as well as the characteristics of stable student groups. This is a critical step toward understanding the consequences of student mobility, designing policies to minimize harmful effects to both mobile and stable students, and addressing stresses on schools related to economic and housing instability beyond schools’ control.