Student mobility is a widespread and often unheralded problem facing American schools. The majority of elementary and secondary school children make at least one non-promotional school change over their educational careers, with many children making multiple moves. They do so for a variety of reasons. School changes are most often initiated by families and frequently involve a change of residences due to reasons that are either voluntary (for example, changing jobs or moving to a better home) or involuntary (for example, getting evicted or having a family disruption such as a divorce). But schools can also initiate school changes, such as when students are expelled or when schools are closed. The research literature suggests that changing schools can harm normal child and adolescent development by disrupting relationships with peers and teachers as well as altering a student's educational program. The most consistent and severe impacts are on test scores and high school graduation, with less consistent findings on student behavior. The gravest harms follow from multiple moves and those accompanied by disruptions in the home. Because causes and consequences are varied and complex, recommendations for addressing the issue must be adaptable and applicable to the unique sets of circumstances. School procedures should focus on reducing unnecessary mobility and on making the mobility experience, when necessary, as positive as possible. This policy brief examines the issue first by describing the extent of mobility among students and schools and then by reviewing the research evidence on its causes and consequences. Finally, it offers school personnel and state policymakers recommendations for minimizing mobility and its sometimes negative consequences. (A list of notes and references is included.)