What causes school violence three weeks into the school year? So early for deep problems to arise.

You'd think they'd at least wait until after Spring Break. 

Summer grudges.

The 'roots' of such violence may well go far deeper than a mere 3 weeks (plus a summer holiday).

Clash of personalities, I suppose. I remember them happening in September when I was in school, it's nothing new.

Brilliant answer, WB. Especially that last part. :)

Another brilliant observation, WB. You're a genius. :)

The kids have memories.  If they do not move around they go to school with the same children year after year.  They remember if so kid was  a bully or was mean in some way.  Also some kids are just bullies and that is what they do.

probably kids that are violent