Abstract Parental death is one of the most stressful events of childhood and is associated with increased risk for multiple mental health problems as well as impairments in developmental competencies in childhood and adulthood. This study uses a secondary data analysis of a 15-year longitudinal study of a randomized trial of the Family Bereavement Program (FBP) to characterize the developmental trajectories of problems and competencies of bereaved children over six years; to study the effects of the FBP to reduce problem trajectories; and to study how changing these trajectories account for FBP effects on mental disorder in young adulthood 15 years later. The study builds on a major advance in research to assess individual differences in trajectories of outcomes over time following potentially traumatic events such as bereavement. Multiple studies using this method have concluded that the great majority of children and adults have low levels of problems over time and can be considered to be resilient. The current study questions this conclusion which is based on the assessment of trajectories of single outcomes (a unidimensional approach) and does not consider that different people may experience problems in different ways following adversity. Recent research with bereaved adults adapted a multidimensional approach to assess trajectories across five outcomes and found that few adults (only 8%) had low levels of problems across outcomes. The current study adapt this multidimensional approach to assess trajectories of grief, mental health problems, competencies and risk and protective factors over a six year period for bereaved children in a secondary analysis of data from the longitudinal study of the FBP. This is the first study to apply a multidimensional approach to assess individual trajectories of four domains of outcomes (grief, mental health problems, developmental competencies and risk and protective factors) of children following any major adversity. The findings have significant implications for understanding which bereaved children who could benefit from evidence-based services. The study will apply the multidimensional approach to assess the effects of the FBP on trajectories of problem and competence outcomes as well as targeted risk and protective factors over six years. It will also assess the effects of the FBP to improve the aggregate number of problem trajectories across outcomes. Individuals for whom the FBP reduces one or more problem trajectories can be considered responders to the program. The study will also assess how changing trajectories in problems, competencies or risk and protective factors across six years in childhood and adolescence mediate FBP effects to reduce mental disorder, suicidal ideation/behavior or mental health service use nine years later when participants are young adults. Findings from these analyses have action implications to optimize effective dissemination of components of the FBP that target media...