Modeling trajectories of physical aggression from infancy to pre-school age, their early predictors, and school-age outcomes.

This study identified latent trajectories of physical aggression (TPA) from infancy to preschool age and evaluated (a) effects of early parent, parenting and child predictors on TPA as well as on social, behavioral, and academic functioning in Grade 2, and (b) TPA effects net of early predictor effects on Grade 2 functioning. We used data from the Behavior Outlook Norwegian Developmental Study (BONDS), which included 1,159 children (559 girls). Parents reported on risk and protective factors, and on physical aggression from 1 to 5 years of age; teachers reported on Grade 2 outcomes. We employed latent class growth curve analyses and identified nine TPA. In fully adjusted models simultaneously testing all associations among predictors, trajectories, and outcomes, maternal and paternal harsh parenting, child gender, and sibling presence predicted TPA, which significantly predicted externalizing and academic competence in Grade 2. Child gender had a pervasive influence on all outcomes as well as on TPA. To our knowledge, this is the first trajectory study to determine which predictors are most proximal, more distal, or just confounded, with their relative direct effect sizes, and to link early paternal as well as maternal harsh parenting practices with children's TPA. Our findings underscore the need to include fathers in developmental research and early prevention and intervention efforts.