“How do you tell the difference between an energetic child and ADHD?” --About.com Reader
Lots of people think of ADHD as the proverbial hyperactive child in the classroom, running and jumping around with lots of energy and enthusiasm, but ADHD is much more complex.
The core symptoms that define ADHD do include hyperactivity, along with impulsivity and inattention. Not all kids (or adults) with ADHD will have these symptoms in the same way or to the same degree, and you will certainly see changes in the way the symptoms manifest or present as an individual moves through different stages of life.
In regard to your question, it is important to recognize levels of impairment. So it’s not just that a child is energetic and active -- rather, there is a chronic, pervasive problem with the child’s ability to regulate his or her activity level, as well as impairment in the child’s ability to inhibit and control impulses. The impairment of functioning or learning is the key to differentiating ADHD from normal activity.
Hyperactivity and the other primary symptoms, impulsivity and inattention, are really just the tip of the iceberg for kids who have ADHD. There can be additional impairments that may not be as obvious –- things like difficulty processing information. With the hyperactive example, it may be that the individual has trouble slowing down enough to process information accurately. He or she becomes frustrated and overwhelmed very easily, has trouble regulating emotions, and struggles with executive function issues like organizing, planning, prioritizing, paying attention and remembering details. Kids with ADHD also tend to be less mature developmentally.
So as you can see, for a child with ADHD, there is much more involved than simply being active and full of energy.
Read more about the symptoms of ADHD.