Hello Charlot,
I rarely have challenges from students that are in cliques. However, I do understand your points. I've told students that cliques can be somewhat harmful, simply because if one student in the clique does something negative, the other students in the clique feel as though they must follow suit. I had a clique of three young ladies. One of the young ladies in the clique decided to dropout of school, and the other two young ladies in the clique dropped out as well. You do have to watch cliques.
Patricia