There are groups that misbehave in every mesivta HS, regardless of whether it is yeshivish or MO. Switching schools may be an option, but this really isn’t the kind of topic that should be discussed in a public forum, or based on the little known or understood about this particular young man.
Speak with his principle, speak with your rav, speak with experienced educators and daven. Keep the lines of communication open and show him unconditional love. With siyata dishmaya, this will become a growth period.