From the actions you describe about your son many are symptoms of ADHD. The low self-esteem is more of a result of suffering from these symptoms, he has no control over most of these actions and being 12 years old he has probably spent much of his childhood being criticized, disciplined, bullied, treated as an outcast because he is different. I went undiagnosed until I was 38 (53 now) and up until then I was considered lazy, stupid, unmotivated ect. Little was known about ADHD when I was a kid so basically my childhood was a living hell. What you should do between now and your sons Dr. appointment is read up on-line as much as you can about ADHD, you need to educate yourself and understand what it is and what your son has to go through. Is the doctor your going to experienced with ADHD? That will be a major issue in getting your son properly diagnosed and a proper treatment program. I would also keep much of your sons issue with ADHD to yourself/spouse and teachers. There are many people who don't believe ADHD is a real disorder or blame it on diet, bad parenting, ect. What you don't need is someones unsolicited opinion or advice as it will only make it more difficult and confusing to go forward with the right treatment. Although medication is not a cure it is an important part of a treatment plan. If I had the opportunity to be put on meds as a child I know for a fact that my life would have turned out much different, for the better. It's made a huge difference in my quality of life, but still suffer from the effects of going undiagnosed most of my adult life. But as I said educating yourself is the key to help your son, there are many great websites where you can get valuable information. I can tell you right now that your son is most likely extremely frustrated about his actions and behavior. People with ADHD are not stupid or lazy, far from it, most likely he has a very high IQ. Our brains are wired differently, we process information much differently than so-called normal people. Telling him things like "try harder" or "why can't you be like other kids" will only make him more frustrated. Dr. Ned Hallowell described ADHD this way to a young kid he had just diagnosed with it " A person with ADHD has a brain of a Ferrari, extremely powerful and complicated, but has the brakes that belong on a bicycle" . I will tel you this ADD is real, it's a real disorder and you did nothing wrong to cause it. Chances are either one of the parents have it.