The development of physical aggression from toddlerhood to pre-adolescence: A nation-wide longitudinal study of Canadian children

The objectives of the study were to model the developmental trajectories of physical aggression (PA) from toddlerhood to pre-adolescence and to identify risk factors that distinguish typical (normative) from atypical developmental patterns. Ten cohorts of approximately 1,000 children (n = 10,658) drawn form a nationally representative (Canadian) sample were followed over 6 years. Using a group-based trajectory approach, we identified three groups of children with distinct developmental trajectories between 2 and 11 years of age. One third of the children (31.1%) followed a low desisting trajectory, reflected in infrequent use of PA in toddlerhood and virtually no PA by pre-adolescence. The majority of children (52.2%) followed a moderate desisting trajectory, reflected in occasional use of PA in toddlerhood and infrequent use by pre-adolescence. One sixth of the children (16.6%) followed a high stable trajectory of PA. Multivariate logistic regression indicated that children in the high PA trajectory group were more likely to be boys (OR: 1.67; CI: 1.5–1.87), from low income families (OR: 1.4; CI; 1.27–1.67), from families where the mother had not completed high school (OR: 1.20; CI: 1.05–1.38) and who reported using hostile/ineffective parenting strategies (OR: 1.16; CI: 1.14–1.18). In sum, the results indicate that the typical developmental pattern of PA was one of occasional and declining use over time. However, about one sixth of children, mostly boys fro