in driven to distraction and delivered from distraction (2 pretty good books about ADHD) the doctor says he introduces ADHD to kids as being like having a ‘race car brain’. the brain of someone with ADHD goes really really fast, which is pretty cool and awesome- you have lots of great ideas and enthusiasm and energy and creativity and humour and all that stuff.
but even racecars need to be able to put on the brakes a bit sometimes, otherwise they can’t stop at a pitstop and refuel, or do maintenance diagnostics in the garage (get to sleep at night, sit still and eat breakfast, sit through an exam in class, etc), and they’re hard to drive (they’ll careen all over the place and crash into something sooner or later- just like we will if we can’t pay proper attention, be calm enough and be able to take the time to make good choices, and manage to finish things as well as starting them).
ADHD medication *lets* your brain put on the brakes a little bit easier- it’s like adding a top of the line braking system where there weren’t any brakes before, so the car can run properly. it doesn’t stomp your foot on the brake pedal or turn off the ignition or anything silly like that, it just gives you- the racecar driver – a really important ability- to slow the car down a bit when you need to. it gives you a bit more control, so you can brake a little to steer around corners and obstacles better without wiping out, it lets lets you drive more effectively and efficiently (no burning silly amounts of fuel rushing at super speed when you’re not trying to get anywhere in a hurry, or going around the block turning right over and over and getting nowhere cos you can’t stop at the red light on a junction), it helps you to stop long enough to let your engine cool down instead of overheating (rest and relax a bit between adventures, sit still and listen when your teacher is talking)- it gives you enough focus and concentration that you can win the race when you’re *in* a race, but also adds the handling and makes you road-worthy, so you can go for a nice relaxed afternoon cruise on the highway if you feel like it instead of being stuck doing circles on the racetrack all day, etc (helps you to think and behave in the best way for lots of different circumstances- gives you options and choices).
ADHD medication makes your brain work even better than it did before. it doesn’t wreck it- it turns it into a high spec custom model. 
he might sort of get his head around that one. i know i can. 