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Well fortunately he's still underage - under 18. The judge is going to place him in a detention center most probably - away from home and full time at the center. This is somewhat based upon his prior conviction but mostly upon this new altercation. Just the fact that he was involved and admittedly did throw a punch and hit the other kid is enough - it's considered bullying and taken very seriously by the courts of today.
Yes, I would immediately get an attorney - maybe he/she will know the DA and be able to work out a "deal".