From Wikipedia

Group Influence

A T-group or training group (sometimes also referred to as 'sensitivity-training group', 'human relations training group' or 'encounter group') was pioneered in the mid 1940s by Kurt Lewin and his colleagues in what became The National Training Laboratory (now known as NTL Institute www.ntl.org) as a method of learning about human behavior. First conceived as a research technique, the t-group later became a new type of pedagogy. According to its founders, in T-groups, participants themselves (typically, between 8 and 15 people) learn about themselves (and about small group processes in general) through their interaction with each other.

A T-group meeting does not have an explicit agenda, structure or express goal. Under the guidance of a facilitator, the participants are encouraged to share with the group their emotional reactions (such as, for example, anger, fear, warmth or envy) which arise in response to their fellow participants' actions and statements. The emphasis is on sharing emotions, as opposed to judgments or conclusions. In this way, T-group participants can learn how their words and actions trigger emotional responses in the people they communicate with. Many varieties of T-groups have existed, from the initial T-groups focused on small group dynamics to those which aim more explicitly to develop self-understanding and interpersonal communication. T-groups were also of wide use in industry, particularly in the 1960s and 1970s, and in many ways were predecessors of current team building and corporate culture initiatives.

Carl Rogers has reportedly described the T-group as "the most significant social invention of the century". A number of experimental studies have been undertaken with the aim of determining what effects, if any, participating in a T-group has on the participants. For example, a 1975 article by Nancy E. Adler and Daniel Goleman concluded that "students who had participated in a T Group showed significantly more change toward their selected goal than those who had not".