Does your DS 'own' his behaviour? Or is it all 'it's not my fault, the teachers pick on me, everyone else was doing it too'?
To get the treatment you are reporting, it sounds as if your son is being very disruptive. He has the chance of a new term for a new start: be impeccably behaved - all equipment, attentive, no chatting, calling out, calling across the classroom.
You say he is in with a bad crowd, but he chooses his own behaviour. This might not be the sweet well behaved child you had at primary, but it is the persona of your son now at secondary
Do they have a 'behaviour report' system where class teachers have to sign off on behaviour after every lesson and then year head signs it at the end of the day? That might help perhaps?
If your son wants to move then maybe go for it, but it sounds like maybe he needs to do more on taking responsibility for his behaviour.
My DD struggles academically and it is so disrupting when kids call out, make clever remarks, muck about etc. Even so called 'low level disruption' can really impact the learning of others.