“and yes, it is not in my power to change his circumstances,”
So it is not your kid. My misunderstanding of the original post.
“and he’s going to be bar mitzvah soon”
Besides school, does this almost 13 year old hang out on nights and weekends? This is clearly, IMO, coming from the school that he is in. Perhaps speak to someone in the school. If they could care less, the kid is in the wrong school, if as you say you are powerless to change that situation, then dont get involved. Those who can change his situation obviously dont care to (and may not be careful about this either) so dont try to fight them, it will only make things worse. Just continue to be the positive influence that you can be be, and daven for siyata dishmaya.