I had a kid several years ago in the YMCA afterschool program, I worked in at the time, that on his first day was a pure terror. Finally I asked him (he was about 7) why he was constantly being so bad. He said he couldn't help it, that he had to take medicine for it. Seems he had been diagnosed with ADHD and was on Ritalin. I laughed and told him, "What you do, you decide to do, and you have complete control over that." Well, when he realized I wasn't going to let him get by with anything, his behavior changed virtually overnight. I don't know how he acted at home, but when he was in the afterschool program he behaved. He actually became one of my better students, and I was able to rely on him to help out.