Most students change schools at some point in their academic careers, but some change very frequently and some schools experience a great deal of turnover. While many argue that mobility harms students, economists tend to emphasize Tiebout type moves to procure better school quality (SQ). This paper disentangles the disruption effects of moves from changes in SQ. Importantly, it identifies the negative externality movers impose on other students. Student turnover is shown to entail a substantial cost for movers and non-movers alike. This cost appears to be larger for lower income and minority students who typically attend much higher turnover schools.