I coach and taught a lot of swim lessons in the past couple of years and the kids that have trouble paying attention and listening are usually the most rewarding to work with. They make you work for it, but for a lot of the really young ones (I gave lessons to like 2-6 year olds) I feel like it's more of a rarity to have kids who give me their undivided attention.
They're playing in water, their eyes are full of wonder, they feel brave and adventurous. How could they pay attention to me? I don't blame them. These kids aren't hopeless, they learn, it just takes multiple approaches and a lot of positive reinforcement.
I've also worked at a summer camp where we had a really hyperactive camper which made things difficult for the counselors. He came back a few weeks later and the kid was just a ghost. I can't confirm for sure, but I'm almost positive he got put on meds. Now he's just a quiet, obedient little ghost. It's actually sad.