Earth to Janny

We have a 5-year-old commonly discussed in the teachers' office as "The Space Cadet" because even when she's in class, she's never really there. She was recently tested for ADD and we were informed, "She doesn't have ADD. She just has difficulty focusing in class.... And so she won't be treated." To which we all cock our heads to the side and raise an eyebrow. What exactly *is* ADD by the way?