AbstractObservations were made of naturally occurring assertive and defensive behaviors among preschool children, using ethological methods. Four major classes of assertive behavior were studied: attempts to gain possession of objects, personal space intrusion, positive directives, and negative directives; in addition, behavior with aggressive characteristics was studied. The effects of the following demographic factors upon individual frequencies of assertive interaction initiation, probability of defense (to assertive initiations), and frequencies of aggressive behavior were examined: age, sex, birth order, sib group size, ethnic identity, number of parents in the home, father's occupational level, father's education, mother's employment (yes/no), mother's occupational level, mother's education. Results of the multiple regression analyses indicated the most widespread effects for ethnic identity, number of parents in home, age, and sex. The most assertive children tended to be nonwhite/black, older, male, and from single‐parent homes. These results were fairly consistent across all classes of assertive behavior studied. There were only minor effects of social class on assertive behaviors, and the demographic characteristics of the sample indicated that the ethnic differences existed independent of social class. Limitations in interpreting the behaviors studied as indicating an underlying aggressive motivation are discusse