Research shows that by the end of 3rd grade, one of six children in the United States has already attended three or more schools. During a four-year period, overall school stability can fall below 50 percent for many schools. Students--both those who move and those who remain behind--can suffer psychologically, socially, and academically from excessive mobility. Although internal factors, such as expulsion, can trigger these moves, research indicates that external triggers--such as the residential instability of the housing market--predominate. A caring school culture, school awareness programs, improved recordkeeping on student mobility, and strong links between housing and education can help reduce student mobility.