well this is a little late, but there are several things you could do both on ground and in the saddle
On the ground:
Leading over obstacles, or if he's into like combat type boy stuff, make it like a video gave he has. Where he has to go to different "check points". He could either have to name a part of the tack, do something with the horse (curry it, brush it, pick up a hoof) and once he's done with that, he can move on to the next "check point"
That's all I can think of for the ground.
In the Saddle
Barrel racing at the walk in fun. Doing things where he's blindfolded and you tell him where to go/what to do.
Around the world is fun, but that can be dangerous
If you want to keep with his combat type boy stuff thing, you could make each lesson a mission, where he has to get something completed.