What’s more, Parsons, an American education sociologist, put forward the definition of the class in his article that the class actually is a social system with the functions of socialization and choice. From the functional point of view, the class can be seen as a socialized structure and a group institution. These studies have made substantial breakthroughs in the theory of informal groups.

In ancient China, educators usually take "getting along well with others" as one of the evaluation standards of students. And Dai Sheng in the Western Han Dynasty had ever said, “To do the best of your career and to get along well with your friends.” It is obvious to see that ancient Chinese had paid great attention to students' interpersonal communication ability.

The study of informal groups in the field of education was developed with the development of some educational disciplines. In the early 1990s, scholars began to apply the method of sociological research to study the informal group in the school in China.

In The School Management Psychology written by Xiong Chuanwu, it is pointed out that the formation foundation of informal groups is the psychological basis and the space-time basis (1996: 198). The psychological basis is the similarity in the psychological interest, experience, and goals, while the basis of time and space refers to that members share the common free time as well as work time, and they usually have their own space for mutual contact.

Li Wenfen believes that the formation of a variety of informal groups among students shares these three reasons (2002: 82). Firstly, it is formed for the requirement of people’s physiological needs and the sense of security; and secondly, its formation is set up by the member’s social needs of belonging and respect; and the third one is shaped based on the needs of the self-realization.

Wang Yongchun has ever pided informal groups into the hobbies group, the emotions group, and the family group (1996: 43). Besides, according to the relationship between members and the whole collective, the informal group also can be pided into three types – the parental, the deflected and the rebellious.

Li Lingli pointed out that the improper management of the informal group results in the low efficiency of its realization of organizational goals, which leads to the unhealthy development of the group (2004: 52). She made an obstacle analysis of the management communication in the informal organizations and reached a conclusion that education administrators can strengthen the effective communication with informal organizations from three aspects - improving educators’ self-consciousness, narrowing the distance between managers and informal organizations and developing managers' communication skills.

After studying the informal groups in school, Yu Qixian proposed his management strategies (1995: 27). According to the duality of informal groups, we should take the light of its general trend and bypass the disadvantages at the same time. On the one hand, school administrators must make a strict nature distinction of the informal groups, taking the proper treatment towards the different organizations in order to promote these informal groups to step on track with formal groups; and on the other hand, making full use of the advantages of informal groups is also quite significant.

Wang Yifei put forward his corresponding educational management countermeasures (1996: 33). He thinks that eliminating the prejudice and correctly recognizing the informal groups in middle school is the first thing to be done, and we should make the further study and treat the groups differently. In addition, he especially indicates that it is essential to establish the cooperation among school, family, and society.

2.2 The Definitions of the Related Issues

(1) The Group

In short, the group is a concept that corresponds to the inpidual. Behavioral scientists believe that group refers to a community of interdependence, interrelation, and interaction which is formed by a certain number of people for their common goals. Besides, group members share the common values, moral standards, behavior norms and group activities. Social psychologists consider that group is "a human community based on some special characteristics." According to the principle of group composition, the group is pided into formal group and informal group. 某初中非正式群体的现状研究(4):http://www.chuibin.com/yingyu/lunwen_206477.html