This book chapter discusses the problem of transiency, or high classroom turnover, in education. Research shows that a disproportionate number of schools with predominantly low-income African American and Hispanic students have low stability, and that such students are much more likely than white, middle-income students to switch schools in the middle of the year. High student mobility has consequences for students, teachers, and schools (e.g., lower achievement levels, slower academic pacing, and lower teaching satisfaction). Housing instability is a major trigger in moving children out of their classrooms. Poor families move 50-100 percent more often than non-poor families. Welfare reform has resulted in residential mobility. Migrant children typically move from community to community. Foster children often change schools each time they are removed from a home. The federal role in education emphasizes meeting the needs of disadvantaged students, and subgroups who are mobile are among the most disadvantaged. However, the government has taken a very minimal role in confronting this issue. After describing various federal efforts to help transient students, the paper presents recommendations to reduce and handle mobility (federal, state, and local education policies; housing policies; homelessness, welfare, and migrant family policies; and needed research). (SM)