Do you know if he's the subtype with or without hyperfocus? It he's the type without hyperfocus only a few of my suggestions will matter.
Those of us with hyperfocus need to cycle our focus. Focus is not the same as attention. Focus is far more intense. We see the majority as having focus deficit their attention being unfocused and nebulous like a cloud. Where we see that vein on that leaf on that branch on that tree, the focus deficit majority sees a forest. This causes nervousness in a crowd because we look into the eye of one person and read their soul. Then shift to the next person, the then next, then the next ... Members of the focus deficit majority are capable of seeing a crowd as a crowd. Must be relaxing to be able to do that. With us that only happens with eyes shut and white noise like waves in our ears.
Our minds are like a laser cannon with an auto-rotating turret. We can jam on the brakes to slow the rotation a bit but we can't stop it. After a bit we must shift focus or it happens for us. Much of the day I keep a window open here or somewhere else. When I feel the focus about to shift I open this window for as short a time as I can then shift it back to one of the 10 or so work tasks I maintain in parallel.
The strategy is to deal with the laser cannon in a way that looks like a combination of micromanagement plus chaos juggling. Have the learning materials there. Point the focus on one for a bit. When it snaps point it at the next topic. And so on cycling among topics. Without the option of other input.
Most importantly turn off the TV. Power off, blank screen. Really. Not powered on. No discussion on it. The TV's moving image tends to allow the laser cannon to focus on the image and the commercials are timed just right so the snap goes from show to commercial then back to the show so he never snaps away from the TV. TVs are hypnotic to us and must be powered off. Does not matter if TVs are not hypnotic to you. Broadcasters know exactly how the hyperfocus of ADHD folks work and how to make it work with the focus deficit majority as well.
But think about why the TV is hypnotic to us. Watch the timing of the commercials and how that works for us. Allow the shift from topic to topic in studies to happen like that. Several books open on the table at once shifting from one to the next every several minutes like the timing of commercial breaks on TV. Don't bother trying to understand why it works just try it and see how it works.
Teach this for testing skills - Every few minutes close his eyes and picture his calm place. The beach or a fishing boat or whatever. Some timer to vibrate every 5 minutes if he tends to zone out too long at these points. Then several minutes back on the test. Back and forth. Use the hyperfocus to excel on the part of the test worked on during one focus snap. Then on relaxation on the next focus snap. Then back to the test. "Lather, rinse, repeat" as it says on the shampoo bottle.
In sports go with one that requires a constant shifting scan not a more nebulous awareness. The scanning aspect of soccer with the constant changes on the field. The brief plays of football followed by the difference of the huddle. The long walks of golf, not so much. Some like the focus aspect of each throw in bowling though. The long waits in baseball, not popular with most of us ADHD folks. The speed of hockey or lacrosse, that's the stuff ...
For exercise - Aerobic beats resistance. Something about how the oxygen flow effects the hormones effects the brain milds out the snap. A night time run works great and just happens to train for soccer. Just sayin ...
Mediation - Seems like it would not work. Doesn't for some of us. Works great for a lot of us. This part works also for the ones without hyperfocus. Must have unmoving visual field in front of us, though. Power off that TV. Yep, I repeated that a bunch of times for a reason.
Medication - Try coffee. Stimulants for the majority are depressants for us. If coffee wires him, he does not have ADHD. If coffee relaxes him he does. This part works also for the ones without hyperfocus. If the caffeine in coffee helps be open to other medications otherwise do not medicate.
Above I called it micromanagement. Nope. It's focus direction. Look at this topic. Snap. Now look at this topic. It's cyclical regular management. Above I called it chaos management. Nope. It's working with the dance of the snapping focus. It's a dance among topics diving deep into each one in the process.