This is a multi-method, longitudinal study of the role of early adversity in the development of school readiness, which has clear theoretical, educational, clinical, and policy implications. We propose to assess the unique and interactive effects of family adversity (e.g., harsh and inconsistent parenting, low income) and peer adversity (i.e., peer victimization, peer rejection, and friendlessness), on the development of multiple indicators of school readiness (academic functioning, executive functioning, and social behavioral skills) that are critical for a successful transition to school. Further, we will examine whether early family and peer adversity “get under the skin” by altering stress system functioning, as measured by the hormone cortisol, and whether stress dysregulation in turn impairs school readiness. We will test the legacy of early experiences on kindergarten school readiness, beyond the role of ongoing adversity. Data will be collected from 400 children diverse in SES and race/ethnicity across the transition from preschool to kindergarten. We will use multiple methods (direct academic assessments, cortisol, caregiver and teacher reports) to assess early predictors of school readiness across this significant school transition. The current proposal will use advanced techniques including hair analysis for cortisol to obtain an index of chronic stress exposure. Investigating the unique and interactive effects of both family and peer adversity provides a critical next step in research on the biological embedding of early adversity and its consequences for the transition to school, as few studies have examined the role of both family and peer processes in dysregulated stress system function or school readiness. Understanding these pathways to school readiness is critical to informing content and timing of preventive interventions. The proposed project will provide a rich dataset with opportunities for additional exploratory analyses related to directionality of associations and gender moderation. The proposed project is well positioned to advance a major initiative of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (Child Development and Behavior Branch): Advancing research on the psychological, psychobiological, language, behavioral, and educational development of children.