I agree with emy, as it's unacceptable if it continues and the school can't contain it, but thought it worth throwing down a few slightly more optimistic thoughts for you.
First is that DS had a child like this in reception. (Chair throwing at one point.) School worked with him and though he still has his moments (Yr1), he's stopped hitting and fighting. The school handled this boy really, really well though and I can see it could easily have gone the other way.
Though I didn't really want DS to see that level of aggression, in a way it was a positive, because it's part of life to be able to learn how to deal with all situations/ people. DS learnt a lot by seeing how the teachers dealt with it, how to behave when this boy kicked off, etc, so in lots of ways it wasn't all negative.
There might well be a SN aspect to it, which if there is the school should be onto and sorting help for him. Again, depends on how the school handles it - ie does it see SN as a problem to be buried, or do they embrace it as a positive. Big difference between schools imo.
Final example I promise, but another boy in DS's class has profound autism. He gets aggressive if anyone's upset as he can't handle it - ie it upsets him and he loses control. This boy has a 1:1 helper, and the children take it in turns to play with him, have learnt what his triggers are and though this boy shows some violence, the children have all seen past that to the real person. When he loses it (and it's scary, I've seen it), the kids step back/ fetch an adult and handle it maturely and well. Again I think that's a valuable thing and am really glad the boy's part of my son's class.
Have you got a parents' evening coming up though? Why not add it to your list of questions. You may be encouraged by what they say. Hope you are.