Is he verbal? Could acting out be his only way of demonstrating his dislike of something? If so, he needs a way to communicate dislike, and his need/desire to be removed from certain situations. I'm working on that with my oldest daughter.
If it is happening when the child is put under pressure then they need to put things into place to addess this.
For example, have they taught him how to recognise his own emotions and the emotions in others. Have they taught him how to judge where he is on a level up to 10 and 10 is errupting like a volcanoe. Have they taught him how to use a quiet place to calm down. Has there been agreement between his teacher and this pupils that when he feels that bad he is allowed to leave the class without any punishment afterwards. Does he have any support in class to ensure that he understands the language and what he is expected to do. Have they looked at the classroom environment to check that there is nothing that is causing him to become anxious/stressed/over stimulated from a sensory point of view.
Any animal, if they feel cornered or threatened will attack. Humans are no different. What options are they offering him as a way out. Are they meeting his needs and supporting him in school (both in the class and during breaktimes/dinnertimes?).
If he has learnt that by being violent he is removed from the class/teacher and goes to the head, that in itself is behaviour he has learnt that gets him out of a stressful situation. Ie. if he cannot cope and becomes distressed, if he is violent, he is removed from that situation. That is reinforcing the violent behaviour.
The school/teacher need to be doing more to teach him other ways, as mentioned above, and the teacher/school need to be more sensitive to what they are expecting from him and whether he can achieve that.