Am I the only one who finds this pretty normal teenage behaviour? Don't confuse that with excusing it, allowing it, or encouraging it, but it's pretty normal from a human historical and developmental perspective. Adult convictions are unnecessary once the adrenaline stops flowing. You've got kids locked in close proximity with one another, day in day out, regardless of how their personalities mesh, at a volatile time in their development.... they fight.
It probably does happen a lot. In that way sure, its normal. But as you also say that isnt an excuse and should not mean we should brush it aside and allow it. Taking turns beating up a kid several years younger - I dont think Id call that normal.