Re: 9yr old boy biting himself
Did you ever approach him about this? Has he done it since then?
I don't want to alarm you, but it sounds like you have a fairly normal, healthy kid on your hands! He knew not to talk back to his teacher, or to act out in his frustration, so he quietly released his frustrations the only way he knew how to without getting himself into trouble.
Now, would I recommend you encourage him to continue that behavior? Absolutely not! He needs to find a way to be able to release his anger and frustration in a non-destructive way. Deep breathing and counting 1-10, and then 10-1 usually helps. Squeezing his hands into a fist and tightening all the muscles in his body and slowly releasing them as he counts is a help, too. I've heard that scrunching or tearing up a piece of paper can help, but I'd worry that it might end up being a sheet of homework or other important school paper that got torn up, and that wouldn't help anything!
It's something you might want to talk to his teacher about, if you haven't already. The teacher might have better ideas of how a kid can release anger and frustration without distracting the class or hurting himself or others.