Yes, these kids can concentrate when they want to-sometimes. Sometimes they can't. Only education will help these people work more successfully with our kids. It's another name for a boisterous child. True, kids with ADHD tend to be on the boisterous side, but the cluster of problems which appear when the condition is present are so extreme that they cause considerable problems educationally, socially and in the home.
Boisterous children do settle down over time and learn by experience as they develop.
ADHD kids largely do not. If anything, if left undiagnosed, over time they get worse.