Differences in the social behavior of6-and 7-year-old children of both sexes were analyzed by ethological methods. Observations were made while children attended class in a regular firstgrade school. The incidence of general activity, social interaction, and open hostile activity was higher in boys. No significant differences between sexes were observed in cohesive, ambivalent, and flight components of behavior. Children of both sexes interacted more with girls. These results seem to indicate that gender differences in the way children interact with their peers are more evident during aggressive encounters and that they depend not only upon the sex of the actor, but also upon the sex of the receiver.Research on sex-related issues has hardly been quiescent during the past years. Considerable activity has led to genuine insight into the influence of sex as a subject variable, the contribution of individual different traits, and the pervasiveness of gender stereotypes (Deaux, 1984). What are the main gender differences in behavior , if any, and when do they appear in the ontogenetic development of human beings? After reviewing more than 1,400 published studies, Maccoby and Jacklin (1974) concluded that very few sex differences have been substantiated. Their conclusions, however, have been challenged by other authors (such as Block, 1976).Although numerous situational factors appear to elicit or minimize gender differences (Frodi , Macaulay, & Thome, 1977), sex-related phenomena cannot be qualified merely by "molding" situational pressures . They are also influenced by individual biological constraints and by personal choices based on past interactions and future expectations (Hinde, 1982(Hinde, , 1984 Hinde & StevensonHinde, 1976; Mendoza & Ramirez, in press;Ramirez, 1978Ramirez, , 1984, and ultimately they are understandable only if analyzed in the context of social interaction (Dunn, 1976). As Hinde Hinde, Easton, Meller, & Tamplin, 1983) pointed out, individuals behave differently according to where they are (social situation), whom they are with (presence of adults, and even of different kinds of peers), and their own individual characteristics and cultural backgrounds (social class, ethnic group values and norms , and expectations). In sum, human relationships vary in a complex way.Social interaction could be assessed in a variety of ways, such as by reports, verbal interviews or questionnaires, and direct observations of behavior. Verbal interviews alone provide a relatively poor index, especially at early ages, and laboratory observations of a selected subject population are not exempt from constraints and pressures; for instance, as Eagly (1983) observed, these experimental situations may emphasize the subject role to the exclusion of more complex sex-related roles that may be prevalent in the field, and may even put more stress on what a subject can do than on what he or she will do, given free choice , in a more natural environment. Therefore, the essence of ethological research must be to observe, to n...