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I find it interesting that they diagnosed him with a mild case of ADD, but his major problem seems to be rages with some depression and anxiety, and he is being treated with a bipolar medication (which seems to help him). Has anyone mentioned bipolar disorder to you? A book that has helped many people here with rages is the explosive child by Ross Greene. I am also enjoying his other book on collaborative problem solving. The bipolar child is also a very good book.
http://www.bipolarchild.com/
They have this website. You might want to do some reading and see it anything fits. There is also a link on there to a questionnaire from the juvenile bipolar research foundation.
Sometimes young children are difficult to diagnose and it seems that a first diagnoses is quite often ADD. Stimulants can make kids much worse if they are bipolar.