The forming–storming–norming–performing model of group development was first proposed by Bruce Tuckman in 1965, who mentioned that these phases are all necessary and inevitable in order for the team to grow, to face up to challenges, to tackle problems, to find solutions, to plan work, and to deliver results.
Read this Wiki entry for a simple and easy to follow overview click here
This Youtube video provides a nice introduction to the theory click here
Here is the handout we used in the staff meeting click here
A Mindtools pamphlet on how to support movement between the group stages Click here