Rudolph sorry to hear about this problem, it must be distressing for all concerned.
I totally agree with tethersend 'Show that you are on board with helping the school to find the reasons for the behaviour...'
At times it is frustrating dealing with school but if you co-operate with sensible, helpful suggestions and provide alternatives to any unhelpful suggestions you will (I feel) get the best from the teachers. It must be a very hard job being a teacher and dealing with all manner of things in school and so to meet a parent who is helpful and wants to co-operate must be so much better and easier to work with than someone who is in any way 'hostile' even if you have good reason to feel anything other than co-operative! These are generalistaion Rudolph and not about you.
Please ignore me if this is really obvious but do you praise your son when he has a day without hitting, not by saying well done for not hitting (of course) but maybe something like 'It's so good you had a fun day and got on with all the classmates, you must be very proud of yourself" etc.
Also, again, ignore me if you have tried this but have you asked your little one why he hits?
Have you asked him if he wants to stop hitting?
If he does want to stop (even a little bit) have you asked him what he suggests might help him to get along better/not hit etc at school?
There is an excellent book called 'How to listen so children will talk and talk so children will listen.'
www.amazon.co.uk/How-Talk-Kids-Will-Listen/dp/1848123094
One of the things it suggests is talking in a really simple and listening way with lots of pauses and gaps in the conversation so the child can supply their own thoughts. Not bombarding them with questions but talking about the situation in a way that they feel they can contribute something.
It also allows for things like fantascising (can't remember if the book used other words for this) so they might say "I hate it when everyone crowds in."
You might say "Oh I just wish you could fly up right out of the scrabble of children. (pause) It's a shame you can't. (pause) What could you do to make it feel better when everyone is crowding in."
Now as an adult we might say 'hang back to the end' or 'get to the thing first' or 'ask teacher to get the game I want for me' etc etc.
But the child might have an alternative idea which would work for them.
If this does prove to be the problem then you could realistically ask the teacher if the children could come up table by table to get toys of coats or whatever. Not necesarily all the time but some of the time, especially if discover (using tethersend idea of monitoring to see when it happens - e.g. if it is always at the end of class when he is tired etc then that would be a prime time for the teacher not to encourage a rugby scrum for toys or games!). If you or the school have kept any record of these situations that occur you may already know when it is happening.
EG if they only do PE once a week and it happens every time they may need to allow a bit longer for getting changed so less stress. If they have PE every few days but it only happens on a Friday then maybe he is extra tired by Friday. My friend's son was very stressed by changing for PE because there was an element of competition in it. Whoever could get changed fastest! Where are some kids would love this and it would get them moving faster others found it a real pressure which was just too much to cope with in addition to all the other things!
Here are some of the ideas when having the conversation....
Accept their feelings.
Listen with full attention.
Acknowledge their feelings with a word – “Oh,” “Mmm” or “I see.”
Non-judgmental listening
Give their feelings a name.
“I can see you’re frustrated.”
Give them their wishes in fantasy.
“I can tell that you didn’t like the movie. I’ll bet you wish you had seen ‘Wall-E’ instead.”
When you give a feeling a name, also be specific.
To show empathy – that you understand.
Don’t say, “I understand…” because you probably don’t.
Respond with “The movie was a little scary in the part where the transformer was blown up.”
Don’t repeat exact words back, rephrase.
Don’t repeat the names they call themselves.
No: “You’re not so dumb because it took you three hours to do your homework.”
Yes: “It must be discouraging when work takes longer than you expect.”
Some highlights from this brilliant book are available
here
Stay calm, you will get through this, do tell us how you get on. I may be in your boat soon so I would welcome advice if I am!