Trajectories of aggression from toddlerhood to age 9 predict academic and social functioning through age 12.

Background: Using longitudinal data from the NICHD Study of Early Child Care and Youth Development, we examined behavior problems and social and academic outcomes from ages 9 through 12 in children classified into five trajectories of physical aggression, on the basis of maternal ratings obtained from 24 months through 9 years (N = 1195).
Methods: Outcome data were obtained from teacher reports, observations of children's behavior, and children's self-reports.
Results: Children on the high-stable aggression trajectory (3% of sample) showed the most severe adjustment problems, including poorer social skills, higher levels of externalizing problems, and more self-reported peer problems; those on the moderate-stable aggression trajectory (15%) showed poor regulation and inattention. Although children with moderate levels of early aggression that decreased sharply by school entry (12%) appeared well adjusted at follow-up, those who showed a low level of stable aggression (25%) evidenced some unanticipated social and behavior problems. Children in the contrast group (45%) were consistently very low in aggression from toddlerhood onward.
Conclusions: Results highlight links between different patterns (stable or decreasing) and levels (high, moderate, low, very low) of aggression across childhood and children's later adjustment. For example, even quite low aggression that is stable appears to be a risk factor for some social problems; in contrast, moderate aggression that decreases sharply to no aggression by school entry is associated with good adjustment at age 12.