J. Richard Hackman, a Harvard University professor of Social and Organizational Psychology and co-author of Senior Leadership Teams: What it Takes to Make Them Great (as well as author of many other classics in social pyschology), in an interview for Harvard Business Review, said this about teams:

People tend to think that teams are the democratic—and the efficient—way to get things done. I have no question that when you have a team, the possibility exists that it will generate magic, producing something extraordinary, a collective creation of previously unimagined quality or beauty. But don’t count on it. Research consistently shows that teams underperform, despite all the extra resources they have.

This observation is based on research that Hackman and others did on over 120 executive teams in a variety of organizations around the world. They found that the vast majority of these team members did not know who was on their teams, what the team purpose was, and how to be successful as a team. I think these were teams in name only. If they don't have a clear, specific purpose to which everyone in the group is committed, then they don’t have a team. Using a sports analogy, as people are apt to do when talking about teams, it would be like bringing 10 people together to play a game without telling them what game they are playing, how they will keep score, and how they will know when they win.

I have no doubt Hackman found a preponderance of dysfunctional executive groups. That has been my experience, too. Groups of managers are brought together, called a “team”, and expected to “produce something extraordinary.” That isn't enough to turn a work-group into a high performance team. I like Katzenbach's and Smith's definition of a team:

...a small number of people with complementary skills who are committed to a common purpose, performance goals, and approach for which they hold themselves mutually accountable.

Somebody has to lead group members in the hard work of clarifying membership, developing commitment to a common purpose, establishing performance goals, and holding each other accountable. Then, and only then, might they have a chance of doing something extraordinary together.