You have tried some great things!!!
Here is something that might work:
When he hurts a friend, do you go directly to him or do you put your attention on his friend? What we put our attention on just gets bigger!!
So if he hits, start doing this:
Go directly to the child that he hit and put your arm and warm words to that child. then, instead of excluding your child bring him into the situation and do some empathy training as well as empowering both children. here is an example of what i mean:
"Johnny, are you ok? You look really upset. Chris, come here, look at Johhny's face, Johnny, is there something that you want to tell Chris?...... Chirs,how do you think Johnny felt when you .....? Chris, What is another way that you could have done this without hurtin your friend? Johnny, what do you think about that, what other ideas do you have?"
Does that make any sense? It comes from a curriculum (preschool-100) called 2nd step.
If your child continues to hit, another idea is that instead of putting him in a "time out" put him in a "time away". Pull a chair away from the group, and tell him that you want him to watch how the other children are interacting. If possible narrate what you see. See how Johnny and Jane are working together on that train and how they are talking to each other about what they need? then tell him "when you are ready to work with your friends without hurting them, then come back to the group and show me" then walk away. It may just be a moment, or a minute or 5. the thing is that you have put him in charge.
I guess the things that are important to remember is that your child gets the clear message that hurting someone is never acceptable but that he also gets the tools that he needs to communicate in a way that he is getting his point across. No matter what though, always tend to the child that is hurt first. And if that child is really hurt and needs first aid- ice pack, band aid ...., ask that child if you son can help with the first aid and then let your child get the ice pack, or go to the sink with the child and help them wash off or what ever.
the end result is that everyone in the situation leaves empowered and thier self-esteem intact.
D.-mother of two young adult boys that were wild and crazy and teacher of young children for over 20 years,