In this thesis, I have employed the Social Psychology theoretical framework, collected data, and analyzed data to answer the following three research questions:

1) The definition of the formal group and the informal group and the differences between them.

2) The existing situation of informal groups in a typical middle school, including the reasons for their formation, some typical characteristics, and their general types.

3) The different effects of informal groups on students’ development.

    4) Suggestions on how to deal with the informal groups in middle school.

2. Literature review

2.1 Research both at Home and Abroad

Much of the early work on human social behavior focused on groups. In fact, the earliest empirical undertaking in the field was concerned with why people perform differently in groups, as compared to in the independent study situations (Triplet, 1898). 

In 1924, the American psychologist professor George Elton Mayo began his eight-year "Hawthorne Experiment", through which he found that there were various forms of informal groups in the enterprise in addition to the formal group (Cullen, 1992). Mayo first proposed the existence of informal groups in the organization, and he believed that people are social people, so social interaction and interpersonal relationships are the most important needs of the human race. Based on interpersonal relationships and taking emotional as a link, the organization will inevitably form informal groups. These groups will have a significant impact on the efficiency of the organization as well.

Mayo argued that informal groups are spontaneously organized in communications among different people. Because of common interests, common feelings and common goals, different persons are formed by voluntary coordination. It is not like a formal group which is usually in a stable and balanced state, but in a continuous adaptation where it continues to reassemble them.

Following the Hawthorne experiment, people have conducted more in-depth research on informal groups and try to give various kinds of definitions of informal groups from different perspectives. The early social psychologist McDougall used instinct to explain the gregarious behavior and gregarious tendency of people, and he concerned the instinct as the promoter of all human activities. 

In the 1930s, the American psychologist Moreno proposed an experimental method – “sociometry method” that mainly focused on the mode of interpersonal interaction within small groups and the status of members' interpersonal relationships within the groups. Besides, concerning from the ways of personal contact, Cooley believed that a person first comes into contact with his family, partners, and neighbors, and it is a face-to-face, direct, and closely related group in which one is able to acquire sociality and personality. Consequently, he called it the first group (the personality group).

American social psychologists, such as Bells, James, Moreno, had made discussions on the causes, characteristics, types, and functions of the informal groups from various perspectives of the constructions of companies, schools, and classes. And the sociologist and psychologist K. Davis had pointed out, “informal organizations are not established or needed by formal organizations, but spontaneously established by the networks of personal and social relations as well as their interrelationships." According to the general sociological point of view, informal groups refer to the groups of the spontaneous formation based on personal likes and interests, and there is no fixed goal, status, and relationship between members. Besides, Levine, Moreland, and Choi had discussed that motivation to join groups and to remain a member, and motivation for groups to recruit and retain members are important constructs in group socialization theory (Michael, 2001).