There are many ways to form small groups for learning activities. One tool that I like for its flexibility is to give each participant a playing card, then form groups on the basis of poker hands (or some other game): Four of a kind, Flush, Straight, Straight Flush, etc.
You can have face cards (or any other set) be observers or note-takers. You can have jokers be facilitators. You can form groups of any size.