If reasonable force was used in response to a punch I do not have an issue with.
However reasonable force to a punch is not slamming someone on their head.
In my opinion slamming someone on their head is lethal force because the intent is to cause serious bodily harm.
The Bigger kid could have run away the Bigger kid could have responded in a non violent way and just restrained him, could have told a teacher and could have used reasonable force to defend himself.
First of all, "reasonable force" is subjective and is debated amongst highly intelligent and educated military, law enforcement, political/diplomatic and elected officials. Expecting a 13 year old kid to get it perfect is silly.
Second, you say "in response to a punch" but there were multiple punches, and since the posting new info has come out, namely that this treatment has been ongoing for a year. Is a body slam a reasonable response to 365 punches to the face?
Third, to assert that just because he slammed him he must have had lethal intent is pretty presumptuous, and I would suggest, highly inaccurate. He slammed him because he is big. Small and quick fighter darts in and out punching, big slow fighter gets hold eventually and throws.. that's pretty much their best genetic options, which is why its the common tactic for both.
Fourth - this is where many people miss the point when it comes to bullying. You are comparing the physical actions and the potential physical injury of each kid, and so it is easy to say body slam > punch.
This is faulty logic however, because the damage caused by bullying is NOT PHYSICAL. It is the emotional damage to ones self esteem and confidence that is at risk.
I have owned my own company for years. We are contracted by many other companies who need help training, motivating their employees etc. EVERY LONG TERM SUCCESSFUL AND HEALTHY PERSON I have worked with had a solid self esteem and good helping of confidence. Every truly happy person I have met had the same. It is one of the common traits amongst them all. Want to know the common trait in most under-performing, unhappy, unsuccessful people? Its the same for people in co-dependent and unhealthy relationships - low confidence and low self worth.
Now with that information, we can look at it this way; body slam < multiple punches AND humiliation that is damaging his self esteem and self confidence, thus damaging his chances at long term happiness and success.
Is there a reasonable force problem in that context? Nope.... Bruno and I are in agreement.... my children will get rewarded for standing up to a bully in defense of themselves, or any other person being bullied, and they would have to do a lot for me to think their response was too violent. Attempts at taking from them their self respect, self confidence and self esteem can and should be met with heavy and swift response.
My 18 month old already works the focus mitts.... If any of my kids are caught using these skills to bully there will be hell to pay - but they are well aware that using their skills to stand up for others isn't just ok... it's expected.