Preceded by Social Identity Theory (SIT), proposed by by Henri Tajfel and John Turner, Social Identity Development Theory (SIDT) focused attention on how cognizance of in-group and out-group differences affects child development. SIT theory asserts that adults adopt attitudes and preferences regarding group distinctions. Additionally, people tend to categorize others, often stereotypically, on the basis of the fact that they do not belong to one's in-group.
Prejudice is a learned phenomenon, according to SIDT. During a child's earliest years of life, she experiences an undifferentiated phase, in which she does not make many in-group/out-group distinctions. Rather, she may simply recognize that she shares certain things in common with other children who are near her own age, regardless of whether or not they belong to the group that she functions within.
During the ethnic awareness phase of a child's development, which usually occurs as he advances beyond 3 years of age, the child will begin to differentiate himself from others on the basis of certain markers. For example, he will recognize that he, unlike his sister, is a boy. He may observe that his hair is brown instead of blond. He may even begin to make distinctions on the basis of ethnicity, such as African-American, Asian, Mexican and Caucasian.
Children are likely to prefer participating as a part of an in-group within which they have been raised. Thus, if a Chinese-American child born to Chinese parents has been raised within an in-group that favors Chinese and Chinese-Americans as members, she is not likely to break away from this group to participate in an altogether different group. Fortunately, at this phase of development, children may still exhibit an eagerness to associate with others who are not part of their own in-group, on the basis of shared interests.
The ethnic prejudice phase is characterized not only by a child's participation in an in-group but also by negative attitudes and conduct expressed by her in-group members toward out-group subjects. This usually occurs once children have reached 6 or 7 years of age, and is usually supported by a certain degree of adult consent. On the basis of such attitudes, children may make hateful remarks or exhibit hateful conduct toward children who are not part of their own ethnic in-group.