The spawn of a nasty divorce, an arrogantly argumentative teen attends a new school. When senior pranksters torment him, he forms his own clique to counterattack their antics.

The back story description in the logline is unnecessary.
Here it is again with out the backstory:
After senior pranksters torment him, a troubled teenager forms his own clique to counterattack their antics.

This is missing a description of how he intends to counterattack, in other words the goal should be described in the logline. Perhaps even describe in more detail the specifics of his public humiliation so we better understand his motivation for revenge, in other words clarify what the inciting incident actually was.