Hi, welcome to our community. I think we will be able to give you some helpful suggestions.
I am curious though. You said, " I know the reason and do everything I can to correct it." It would really help us to know what the reason for his problem is. So what do you think it is?
Its gotta be kind of maddening that for 3 years you have tried all the standard things (sounds like you have done them pretty well too), and its not working.
Well, let me suggest two things that you haven't (apparently) yet tried.
The first is to add teaching him how to behave instead of punishing him for his actions. There are several good sets of books aimed at the 4 to 7 year old crowd that are meant to be read aloud to them. And then practiced, and reread, and practiced, and reread, and practiced, etc.
A good start might be, "Hands are not for hitting" found here - http://www.amazon.com/Hands-Hitting-Ages-Best-Behavior/dp/1575420775 and if you scroll down you will find other great books.
You can change some of his behaviors by showing him new ones. The hard part is that you have to practice these again and again until they become part of his normal actions.
Annie's post leads to the second thing. When you have tried and tried and its not working then perhaps its something that the child really can't control. This is where a therapist can be helpful. Specifically, he has many symptoms of ADHD. And if he does have ADHD, it would explain why all the things you have tried haven't been very successful. And its possible that he does not have ADHD. If he is the oldest with two younger siblings, it could be an attention thing. It could be sleep apnea. Point being its hard to tell in your short post. I am also the CL in the ADHD forum here -
http://www.medhelp.org/forums/ADD---ADHD/show/175.
If you would like to explore this possibility more - please post over there and I will give you my undivided attention.
But back to other things. What is he getting for breakfast? Fact: Sugar consumption has not been linked to ADHD or even to hyperactivity. However, some studies suggest a link between food additives such as food coloring and hyperactive behavior, but only in about 5% of people with ADHD.doctor. There are cereals with no sugar. I eat shredded wheat minis and add a lot of fruit. If he is not getting a certain amount of carbos in the most important meal of the day - that also could be a problem.
Oh, and just a personal thing. As a young teacher I used to make kids write sentences when they messed up. As I became more experienced, I completely stopped that. Its a huge waste of time. If you want him to repeat something that will help him. Have him role play with you how to do the right thing.
Final question for now - at least. He is 6. Has he been in preschool? Kindergarten? What do his teachers say?
So lots of stuff going on. I don't think we will find answers overnight - but you have been trying for what 3 years - so a few more posts shouldn't be to bad. Get back to us.