ADHD was the most common disorder for children in 2013-14 (8.2%), the most common disorder among boys (11%). These figures are expected to have risen since then. ADHD are often seen together or misdiagnosed as each other since they share many common symptoms.
The internal experience of ADHD has been described to me by kids and teenagers as uncomfortable, busy, chaotic and like a bottle of fizzy drink being shaken. The reason kids and teenagers can't keep still is often that their bodies are buzzing with energy. This is why trying to get them to settle and "calm down" often doesn't work or is very difficult, because they literally need to let out some of that energy first. Shaking their whole body, wiggling, doing a silly dance, running, doing jumping jacks, or going on the trampoline are great ways to release this. You may be asking yourself, but how do we have time for that? BUT, how much time do you spend reminding/nagging them to do what they are supposed to?