It's the nature of young children to have a deficit in their attention and an excess of energy, relative to the levels of attentiveness and activity their teachers and caregivers wish they had. I'm at wit's end sometimes, myself, teaching a class size of one, so I sympathize, but wit's end for the adult does not necessarily mean pathology in the kid. A challenging temperament or developmental stage is not a disorder.
I know there really is such a thing as ADHD, and I have seen what a difference medication can make in the lives of some people who have it. But diagnosing and prescribing for children as young as age three? Come on, people. Sit down, take a deep breath, and reread Piaget.
A preschool teacher who can't return to Piaget as a touchstone should consider maybe changing jobs, or organizing to improve working conditions for preschool teachers. Failing that, s/he might try Xanax to treat Overextended Teacher Disorder.