The transition from preschool to kindergarten has been cited by educators as one of the top educational issues facing the United States (National Education Goals Panel, 1995). Researchers and theorists pursuing this line of inquiry have identified children's aggressive behavior and peer victimization experiences during preschool as critical indicators of preschooler's readiness for school and subsequent adaptation to kindergarten (e.g., Fantuzzo & McWayne, 2002; Ladd & Price, 1987; Pianta & Nimetz, 1991). To date, however, these investigations have focused on forms of aggression and victimization that are most salient to boys (e.g., physical aggression) and they have neglected forms of aggression that have been shown to be more significant for girls (e.g., relational aggression; Crick et al., 1997; Ostrov & Keating, 2004). This has resulted in a significant gap in our knowledge of school readiness, particularly for young females. This is a serious limitation given the demonstrated importance of early school adaptation for children's concurrent and future development (Belsky & MacKinnon, 1994; Rimm-Kaufman, et al., 2000). The proposed research was designed as an initial attempt to address this issue through the continued longitudinal study of a sample of children (n=101; 48 girls) that has already been assessed and followed for two years during the preschool period (preschool study), and that will be reassessed during kindergarten (kindergarten study). Three objectives will be addressed: (1) to examine the utility of preschool relational aggression and victimization for understanding children's adaptation to kindergarten; (2) to assess gender differences in observed relational aggression and victimization in kindergarten; and (3) to examine the stability and trajectory of relational and physical forms of aggression and victimization during the transition from preschool to kindergarten. Assessments will include naturalistic observations plus teacher and self-reports of children's social behavior and experiences and adaptation to kindergarten (social-psychological and academic adjustment).