The psychologist Bruce W. Tuckman came u with a four stage model for group development process. Ten years later Tuckman and a doctoral student added a fifth stage. The stages are forming, storming, norming, performing, and adjourning. Today most people in the OB field follow this model as if it were a fact, however, it is still just a model. The different stages are not of the duration or intensity. Stage one, forming, is when people are still uncertain about their roles in the group and what to expect from the group. people usually hold back and don't give all their ideas or act completely themselves. Eventually, someone will step into the leadership role and get things started. Stage tow, storming, is when people test the leader and see what will be tolerable and will not be tolerable. Subgroups usually form and little rebellions take place in this stage. Most groups stall in this stage because the little rebellions become big rebellions. Stage three, norming, is when the group as a whole sits down and resolves any problems it might be having. It takes someone besides the leader to step up to begin this stage. This is the stage where group cohesiveness is gained. Stage four, performing, is when the group is working its best. people know their roles in the group and thanks to stage 2 there is now open communication among members. The final stage is adjourning. This is where the work is done and the members go back to being independent. It is also the stage that the leader tells everyone what lessons were learned while working together.
I also did some more research and found a site that went into more detail about the five stages and assesses them. It also talks of how Tuckman came u with the model.
Smith, M. K. (2005) 'Bruce W. Tuckman - forming, storming, norming and performing in groups, the encyclopaedia of informal education, www.infed.org/thinkers/tuckman.htm.