Adolescence has traditionally been considered a time of substantial turmoil in the life course, as youth struggle with establishing self-images, finding appropriate and supportive peer groups, and begin their psychological, emotional, and, in some cases, physical separation from their parents. Among the many factors that have been thought to exacerbate adolescent adjustment during this often-difficult period are residential mobility and the school changes that frequently accompany these geographic relocations. Numerous recent studies have found statistically significant and substantively important effects of residential mobility and school changes on problematic adolescent behaviors. Although the observed strength of the association varies across studies and outcomes, recent investigations have reported significant effects of residential mobility and/or school changes on poor academic performance (Ingersoll, Scamman, & Eckerling, 1989; Kerbow, 1996; Pribesh & Downey, 1999), school dropout and low educational attainment (Astone & McLanahan, 1994; Entwisle, Alexander, & Olson, 1997; Hagan, MacMillan, & Wheaton, 1996; Haveman, Wolfe, & Spaulding, 1991; McLanahan & Sandefur, 1994; Rumberger, 1995; Swanson & Schneider, 1999; Teachman, Paasch, & Carver, 1996), drug and alcohol abuse (Hoffman & Johnson, 1998), risky sexual activity, including early sexual initiation and numerous sex partners (Baumer & South, 2001; Stack, 1994), premarital childbearing (South & Baumer, 2000; Sucoff & Upchurch, 1998), and other behavioral problems (Tucker, Marx, & Long, 1998; Wood, Halfon, Scarlata, Newacheck, & Nessim, 1993). However, in many - perhaps most - of these studies, residential mobility is treated predominantly as a control variable, and thus its effects on adolescent development have been under-theorized, and important empirical issues relevant to these associations have gone unexplored. Even when the consequences of residential mobility are the explicit focus of investigation, few studies have attempted to identify the mechanisms through which residential mobility and school changes lead to disadvantaged adolescent outcomes (Fenzel, 1989). Although several observers attribute the deleterious consequences of residential mobility to a reduction in children's social capital (Coleman, 1988, 1990), few studies have attempted to clearly delineate the types and sources of social capital that presumably account for this effect. Moreover, residential mobility among children and adolescents has been linked to other attitudes and conditions, including relations with parents (Pittman & Bowen, 1994) and schools (Entwisle et al., 1997), social stress (Raviv, Keinan, Abazon, & Raviv, 1990), poor self-concept (Hendershott, 1989), and social isolation (Myers, 1999; Vernberg, 1990) that might help to explain its effects on problematic behaviors. Little attention has been given to the possible role of peer networks in mediating the effects of mobility on adolescent behaviors, despite the acknowledged salience of such networks in shaping adolescent behavior (Adler & Adler, 1998). Using the longitudinal National Survey of Children (NSC), the purpose of this paper is to examine the impact of frequent adolescent residential mobility on two key events in the adolescent life course - the initiation of sexual activity and dropping out of high school. Both early sexual initiation and premature exit from schooling have important ramifications for later life. Early sexual initiation, for example, increases the risk period for premarital childbearing and, in turn, places young parents and their children at a heightened risk of social and economic disadvantage (National Research Council, 1987). The failure to complete high school severely compromises later employment and occupational opportunities (Jencks et al., 1972). We give particular attention to factors that might account for any observed impact of repeated residential mobility on these life-course events.