The number of students who change schools in the course of a year or a few years is astounding. And mobility rates keep climbing. Chicago Public Schools, which have long struggled with high mobility, report that 23% of students who entered first grade in 1999 had changed schools by the end of the year. Four years after entering first grade, more than 50% had changed schools, and this is a trend that has continued despite district-wide efforts to reduce mobility, says CPS research analyst Jeffrey Rosen. Mobility is actually the norm while kids are in elementary school, and the exception when they are in high school. This article discusses some of the difficulties faced by high-mobility students, the reactions of schools, and some policies that could be used to reduce student mobility.