Project Summary The goal of the proposed project is to identify risk factors for and maladaptive consequences of friendship dissolution, and, thereby, bolster the scientific foundation undergirding efforts to improve the lives of children with peer difficulties. Children suffer in the absence of friends. How and why children?s friendships end is not well understood, however. Equally unclear are the effects of friendship dissolution and the circumstances in which it threatens well-being. The proposed project is a multi-informant, cohort- sequential longitudinal study of individual differences in friendship loss. Students attending diverse public schools in South Florida will be followed as they navigate the challenging transition from primary school to middle school. Peers, teachers, and children in Grades 3-5 (at the outset) will complete measures describing friendships and individual adjustment 3 times per academic year at 12 week intervals (8 times across 2.5 years). An innovative cohort-sequential design assessing change during an academic year (within grades) and from one year to the next (between grades and between schools) will set the stage for a new generation of analyses that disentangle the causes of friendship instability from the effects. The first specific aim of the proposed project is to identify the antecedents of friendship dissolution. The proposed study will provide the first-ever depiction of factors that predict friendship instability across the transition into middle school, a time when friendship participation foreshadows later social and academic success. Multi-wave assessments will be deployed to determine whether friendships dissolve because of incompatibility arising from differences between partners or because one or both partners possess undesirable attributes that undermine the affiliation. Full longitudinal mediation models will compare competing hypotheses concerning relationship deterioration as an intermediary process: One traces friendship dissolution through heightened conflict, the other through declining feelings of security and support. The second specific aim of the proposed project is to describe the adjustment consequences of friendship dissolution. Hidden among the majority of children who successfully weather friendship transitions are subgroups whose risk for maladjustment dramatically increases with the loss of a friend. The quasi-experimental design (contrasting children who remain friended or friendless over time with friended children who become friendless and friendless children who acquire friends) will offer the strongest possible test of the hypothesis that changes in friendship participation are responsible for subsequent changes in individual well-being. Friendlessness is expected to amplify the ill effects of rejection, because children with peer difficulties possess attributes that make it difficult to form new friendships. Strong repercussive after-effects should also follow the dissolution of long-term, high quality friendships with well-adjusted partners. The proposed project is noteworthy for the novel application of analytic strategies to yield new insights into the correlates and consequences of friendship instability.