I don't know if this "violence" has always been there, or if it's more a "new" thing or an "escalating" thing... but I'm going to assume it's one of the latter two.
Have you had him tested for ALL of the typically co-morbid dxes that go with spectrum kids?
sensory processing disorder (SPD), Developmental Coordination Disorder (DCD), Auditory Processing Disorders (APD), LDs, etc.?
If not... I can tell you first hand that there are three sub-dxes that can drive a kid who is in school, totally insane.
1) sensory processing disorder (SPD) - school may provide sensory inputs that the kid can't handle (too noisy, smells, etc.), or may not provide sensory inputs that the kid needs to cope.
2) Developmental Coordination Disorder (DCD) - not all areas of the world use the formal classification, but it covers a range of coordination disorders, in fine or gross skills or both, that are not explained by other dxes (such as cerebral palsy, for example). Nothing wrong with limbs, muscles or nerves... but the brain can't quite get the pieces together. School success is 100% dependent on functional motor skills at BOTH the gross and fine levels. PE and recess are all about sports. The rest of school is about writing, drawing, sketching, playing an instrument... AND the ability to change clothes fast (including tying shoes...) For the kid with even a minor dysfunction in these areas... school is a nightmare, and the other kids play on this and bully or exclude.
3) Auditory Processing Disorders (APD) - especially auditory figure ground and auditory discrimination. These get missed WAY too often. Many so-called specialists don't even screen for them. But while these two don't make LIFE impossible, they sure make SCHOOL impossible. Auditory discrimination is the ability to distinguish between subtle verbal differences in sound. Auditory figure ground is the ability to hear and pull "forward" those sounds that are important, separate from the "background noise". Classrooms - the best-run ones are simply better than the worst ones - are always full of background noise. Chalk on board, pencil on paper, someone blowing their noise, the hum of the radiator, the teacher who plays background music... but if the poor kid doesn't get the verbal-only instructions right the FIRST time... he's not paying attention, or he's not trying, but either way, it's the KID's fault... NOT. But try and get school to believe you without a diagnosis... (been there done that)
The more you understand the kid, the more you can advocate for the pieces he needs in his IEP, and the more you can figure out can help at home, etc.