Welcome, Jody. We can honestly say, we do understand. While each of us are dealing with different children, there is a great deal in common.
You've had people recommend "The Explosive Child" by Ross Greene. Definitely worth reading, as soon as possible. Maybe yesterday. Get other family members to read it too, or if they can't "get into it", then you explain it to them, because in doing so it helps you fix the understanding of it in your head, so it becomes more automatic.
To get an advance idea on what the book is about, have a look at the discussion in Early Childhood forum.
There are other books and other ideas, but this one is a very good starting point. You may find it is enough, or you may want to fine-tune things a bit more.
What is needed though, is a different way of looking at him and a different approach to parenting. What you are doing right now not only is not working, but it is making things worse. Every time you try to discipline him and you fail, you undermine your authority with him. You are better off not trying, than trying and failing.
There are other ways. And they're actually easier, as well as more effective.
One of the first rules - pick your battles. Do not engage in battle unless you are certain you can win.
Another rule - make it clear he wants to do this. (You may need The Book to learn how to do this).
And again - avoid punishments. Instead, go for natural consequences. So if he doesn't come and have his dinner when he is called, the natural consequence will be a cold dinner. Of course he can always reheat it in the microwave, but it still is a consequence. And it's not something you did to him - he did it to himself.
An example I often give is of a child wanting to run and play outside in the snow, but without stopping to put on a warm coat. You COULD get 'heavy' and say, "You are not going outside, Missy, until you put on your coat! I will NOT nurse you through pneumonia!"
An oppositional child, especially one who is impatient to get outside and play, will be defiant and refuse. If you make a big thing of it, the child would walk over broken glass rather than admit, once outside, that perhaps you were right after all.
So especially with an oppositional child, don't insist.
You can suggest, or you can hand her a coat, or you can say, "Do you want to wear your blue coat or your red one?" This gives her choice, she still feels in control, but YOU have won because she is wearing a coat. She also comes to realise that the suggestion from you to wear a coat is a wise one, and she will increasingly respect you as wise and a resource.
If your child still insists on running out into the snow without a coat, she is more likely to come back when she feels cold, if she doesn't feel she has a point to prove by staying uncoated and cold.
So, back to your son - similar techniques do work because they hand control to the child at a level they (and you) can handle. If he's going to do his own thing anyway, it's best he do it where you can still rescue him, help him out where needed.
The kids who need this most - the ones with poor impulse control, the ones with a high level of frustration, the ones who have difficulty changing form one thing to another. The techniques work on PCs too, so you don't need different techniques for different kids. But some things do need to be customised. The overall principles, though, can apply universally.
On a matter of site techniques - when you reply to someone, you don't have to reply in separate messages to separate people. You can put it all in one post because we all read every post anyway. This should save you some typing and having to repeat yourself.
Also, if you do a sig (like mine, below) it helps us keep track of your basic details - family demographics, etc - so you again don't have to keep telling us. You can update the info at any time.
To do a sig, go to the top of the page and look for "user CP" (top left, I think) and click on it. It should lead you to where you can put in your own info.
You also need to be careful to not put in anything that could identify you or your child - this is for your protection, so you can feel free to dump on us at any time, without the person you're dumping about (the education system, for example) being able to track what you have written and give you a difficult time over it. You might think you would never need to worry - but you just don't know, the time may come when you will be glad of it.
Again, welcome. It's a good team, here.
Marg