The school mobility rate in St. Louis Public Schools was 40% in 2011-2012, meaning that nearly half of students exited or entered a given school midway through the school year. This alarmingly high rate of churning across schools is accompanied by high neighborhood turnover, particularly within low-income, urban neighborhoods. This constant, disruptive change presents a serious and fundamental challenge for urban education. In this article, we summarize the literature linking mobility to educational outcomes, examine the causes of hypermobility in the case study of St. Louis, describe some of the current approaches to this challenge, and propose additional policy and program solutions.