@thirdfiddle
He's working on Debussy's Arabesque no 1 for a school concert - he needs an aim! Four of the five pages are almost perfect, but the second page is tricky. So he's just been stumbling through it until he gets back to familiar ground. I think it's the accidentals in the left hand...
He too is a multi-instrumentalist. His first, I guess, is voice - as a chorister he sings for about 18 hours a week, plus a lesson. He's just got 143 for his grade 6. He also plays French Horn, which has suddenly got loads better with lots of ensemble playing. (Prob about grade 5).
His constant immersion in music seems to have embedded itself in his neural pathways - he can just sit at the piano and compose something amazing off the cuff, or play whatever he's just heard on the radio, by ear, in correct four-part harmony.
So - in common with lots on this thread - the concept of having to actually work at something that he's accustomed to coming so easy to him is alien. He will only do scales, under duress, in the weeks before the exam, and gets a bit arsey with his teacher when he points out the fact he's making loads of errors!
I've never had to make him practise, and don't want it to become a chore, but will suggest the ideas upthread to him to make him feel they were his all along!