Gender schema theory proposes that children begin to form gender schemas (sometimes termed sex-related schemas) as soon as they notice that people are organised into categories of male and female.These schemas are developed through their interactions with other children and adults, as well as the media. They allow children to organise and structure information and to learn about which toys are appropriate for each gender and which clothes are appropriate. Martin and Halverson (1981) describe two types of sex-related schemas: in-group schemas (the group with which a person identifies); and out-group schemas (the opposite group). Once a child has identified with their in-group, they begin to positively evaluate their own group and negatively evaluate the out-group. Children then begin to ignore any information that is not consistent with their in-group schema and this means that gender schemas have very strong effects on what children remember and how they perceive the world.