Age group(s) for which this technique is helpful:
Preschool and Younger
Elementary School
Middle School
High School & Beyond

Primarily used to improve behavior:
Both At Home and At School

Instructions for using this technique:
Transition is hard for most ADHD kids. I've had a lot of luck with "2 Minute Warning". In the morning, I rouse my son up just enough to understand "2 Minute Warning". Then go back to his room after the 2 minutes and wake him up by scratching his head or back, or sometimes by tickling him or an awful rendition of "Oh What A Beautiful Morning." He wakes up laughing at me, which makes the whole morning go better.
I also use "2 Minute Warning" for leaving the house, getting off the computer, etc. I've asked them to use it at school, and at the sitter's I believe it's helped a lot.
When my son starts to blow up, it's easy to see the signs. I stop him, have him take a few deep breaths, and tell me what is wrong. Sometimes I tell him it's not a big deal, it's not worth getting all torn up or getting in trouble with his teacher. (Once he thought his computer game was cheating him. We went back to the instructions and realized he hadn't looed at all the rules.) Sometimes I've had to explain the very obbious to him, very calmly. (He wanted to go home with a friend, but they were gone. "I can't make them be home, we'll try tomorrow.")
He's been able to calm himself down several time. He said, "It's not worth it." His teacher has not been very understanding!!!