It's actually a good question. I think the best insight I got on the topic was reading an article once about how to tell the difference between a child being gifted or having ADHD or being both. This is difficult since they often have similar traits, especially having a hard time completing certain menial tasks. The difference is that a gifted child without ADHD can complete these tasks if he likes the teacher giving him the task, while the one with ADHD will still struggle to complete it despite really wanting to do so.