Why are residential and school moves associated with poor school performance?

Most research on residential mobility has documented a clear pattern: Resid ential and school moves are associated with poor academic performance. Expl anations for this relationship, however remain speculative. Some researcher s argue that moving affects so- cial relationships that are important to ac ademic achievement. But the association between moving and school performan ce may be spurious: the negative correlation may be a function of other cha racteristics of people who move often. We offer several conceptual and anal ytical refinements to these ideas, allowing us to produce more precise test s than past researchers. Using longitudinal data, we find that differences in achievement between movers and nonmovers are partially a result of decli nes in social relationships experienced by students who move. Most of the n egative effect of moving, however, is dice to preexisting differences betwe en the two groups.