48 toddler boys and girls (aged 18-36 mo) were observed in play groups. The assertive acts of each child and the responses of peers and teachers were recorded according to a list of 34 child behaviors and 15 teacher and peer reactions. Assertive behaviors were categorized as hit, push, or kick; take or grab for objects; and verbal assault. Results reveal that the most common type of assertion for both groups was grab or take objects, then hit, and then verbal assault. Boys produced more assertive acts than did girls. Girls’ assertive acts were ignored significantly more than boys. Boys responded more to the acts of other boys than to the acts of girls, while girls responded more equally to the assertive acts of boys and girls. Hitting and taking objects received similar responses from peers. Young toddlers initiated significantly more incidents of aggression, but they were more likely to be brief. Older Ss showed less frequent episodes, but when an aggressive interchange started, it was more likely to continue. Older Ss also responded differentially to various kinds of responses to their aggression. It is contended that responses to assertive acts are information sources for the assertive child. The higher response rate to boys’ acts more often led to reactions from others, while the lack of reaction to girls’ assertive acts gave girls little reason to continue such acts. The assertive acts of 48 toddlers and the responses of peers and teachers were registered. It is argued that the higher response rate recorded for boys’ acts informs the child that such behavior will produce an effect in his world, while the lack of response to girls’ acts suggest the opposite to girls.