Most gender differences happen because of subtle reinforcers given by adults. In one study, researcher Beverly Fagot observed and responded to the findings of what happens when teachers observe "assertive acts" and "communicative acts" of 12- to 16-month-old children. What she found out was there was no difference in the frequency of being aggressive between the boys and girls of the groups. What surprised her about her findings was that the teacher responded more often to assertive boys than to less-assertive boys and more to talkative girls than to the less-talkative girls. This same researcher observed the children a year later and found that a gender difference was now visible. The boys were more aggressive and the girls were talking to the teacher more.
This study explains the development of gender differences through the use of rewarding and imitating. The children figured out that the reward was attention and in turn, imitated the action based on their gender.
Janis Jacobs and Jacquelynne Eccles determined another study that shows the use of subtle reinforcers. They conducted a study of seventh and ninth graders math achievement over time and the affect parental encouragement had on their continuing mathematical education. What they found was that parents often praised their sons with sayings like "You"re a natural math whiz, Johnny!" Girls who got the same grades would get praises like "Boy, you really worked had in math, Janey, and it shows!" The children understood what the adults were not saying: when boys do well it is because they have natural talent, when girls do well, it is because they worked hard to achieve that goal. .
The development of gender differences is explained in this study through outside influences. Although the parents are not intending to voice these stereotypes, they are in fact affecting the performance of their children.
Gender schema is described by distinguishing certain things to be "for" certain genders.