Hi, I am also the CL on the adhd forum here -
http://www.medhelp.org/forums/ADD---ADHD/show/175 - you might want to also post over there if you have additional questions.
Your son is a sharp little guy. Most kids cannot vocalize the idea of closing "the door in his brain". And it is not unusual for kids with ADHD to get tired of trying to explain why they are always getting into trouble and around first or second grade just start lying to avoid the consequences.
His problem is that when you have ADHD, your impulse control center is lacking. You get an impulse and before you have a chance to think about it - you act on it. There are a lot of other things also going on, but at this age - this seems to be one of the bigger issues.
And, it is very difficult to control. What you need to do is to change his normal response. It takes a lot of practice at home (and school).
You didn't say what he was doing at school that was getting him into trouble. There are definitely some things that can be practiced at home to help.
But, you also definitely want to clue in the teacher to his ADHD. There is a lot that she can do to also help. For example, kids of his age can get into trouble for not staying still - yet, for a child with ADHD that is one of the things that they really need to help them focus. Teachers can allow them to move, instead of punishing them for that. It is not unusual for teachers or principals to deny them recess. That is absolutely the worst possible thing to do to change a childs behavior. There are many, many things like that which is different for a child with ADHD compared to a child without ADHD.
What you need to do is to start informing yourself all about ADHD. You are going to become his advocate for a long, long time and you need to understand it.
And once you do meet up with his psychologist do know that all studies have shown that the most effective treatment is both medication and behavioral therapy.
Anyway, just a ton of stuff for you to process and learn about. I am here to help. Please let me know how I can help. Best wishes.