As I observe the various cliques of boys and girls around my children's school, it is clear to me that the cliques are controlled by one child. It may appear that 2 children are in control, but if you take a closer look, it really is one. One child controls the masses. From that lofty position, often that child rules the school. The supreme rulers dictate to the group. The minions then carry out their orders which usually have to do with spreading rumors around the school to humiliate the rulers' targets to either eliminate them as competition or, having already alienated the targets, to keep the targets in their place.
We parents need to ask our children who is in control of their group? Who calls the shots? Are you pleased with the answer? Is it your child? Next, you need to find out how your child is treated in the group? How is your child used by the group? Is your child the one in control of the group? That adds a different dimension to your follow up, in my opinion. Is the group inclusive? Does the leader have a particular DISLIKE for someone in the group? Is their discord within the group?
Our children have free rein at school. No one in overseeing them in the hallways and playgrounds. No one is calling them out on their bad behavior. The rulers of the school are calling all the shots and the targets and other children say nothing not out of loyalty, but out of FEAR.