Abstract: The development and control of childhood aggression have been among topics that received the most attentions from researchers for more than half a century. Especially in recent years, with violence being recognized as a primary and increasingly important public health priority, research in this area has been further promoted and the amount of research has kept rapidly growing.
The last decade has witnessed a transformation of research interest from the average development to the individual difference in the development of aggression, and the extant research indicated that although during middle and late childhood, physical aggression decreases for most children and many refrain entirely, some continue to engage in high level of aggression. Recent person-centered longitudinal studies in western countries demonstrated that children followed different development trajectories in development of aggression and other forms of externalizing problem behaviors. However, empirical evidence on the developmental trajectories of children’s aggression in non-western cultures has been rare.
In the view that systematic information regarding the development of aggression of Chinese children has been highly limited, the present study explored the development and gender differences of aggression during middle and late childhood among Chinese urban children by using both variable-centered methods and person-centered methods. Three specific questions were addressed: (1) the general developmental pattern, (2) the typical developmental trajectories that different children would follow, and (3) the possible gender differences in the above aspects.
Approximately 2000 children from 36 classes of 11 primary schools in Jinan City, Shandong Province were followed from grade 3 (average age 9.26 ± 0.29 years) till grade 6. Children’s mothers reported their aggression on five items from the Aggression subscale of CBCL annually. 1618 students have complete records on at least 3 waves of data collection, among which 1253 students have complete records on all waves of data collection.
The main findings of the study were as follows:
(1) The average level of aggression decreased with age. (2) Three trajectories were identified using semi-parametric modeling, respectively: no aggression trajectory (68.7%), low-decreasing trajectory (26.8%), and persistently high aggression trajectory (4.5%). Both the low-decreasing and persistently high aggression trajectories differed from the no aggression trajectory on measures of peer acceptance and peer rejection at age 12 indicating that the two aggressive trajectories were associated with interpersonal maladjustment. (3) Both multinomial Logit modeling and Chi-square analysis indicated, compared with girls, boys were more likely to be classified into trajectories of low-decreasing trajectory and persistently high aggression trajectory. However, this did not mean girls did not experience high risk of aggression, in fact 2% girls were identified to be persistently highly aggressive children. The implications of these findings for aggression and violence intervention and directions for future research were discussed.

Key words: aggression, normative developmental trajectories, group-based developmental trajectories, gender difference