Practice is overrated....
Well ok maybe not but what many kids consider practice ie playing pieces from start to finish and saying " done" ...
I'd hope at grade7 your ds has had a really solid " how to practice" grounding ie find the the tricky bits, break them down - even to just getting between two or 3 notes then teach your body to play that (depends on the instrument as to what you need to " teach your body" it might be swapping fingering by thinking exactly what fingers go up and which down, it might be how the breath feels when the sound is right etc) before moving onto anything else. Then add a note or two to the pattern but never allowing anything other than perfection for fear of " learning the mistakes" .
There is clearly much more to it that I know, but it's possible by picking the difficult bits, and beating them, to get a piece worked up in a short time.
Certainly my gang don't believe in over practicing , but practice properly when they have to.
At 11 I'd suggest a combo of work on really focussed short practice and just enjoying ensembles / orchestras or what ever- make lots of music! Whilst taking pressure off him, unless he's actually got a burning ambition to be a career musician.
I might also have a word with his teacher and think if he needs to step off the exam treadmill for a bit. Exams are always better approached " from above" when the skills needed are really well within your capabilities. Our 1st study teacher really doesn't set much store by exams - they almost have to plead to do one! Maybe leave grade 8 year or two unless he " must" do it for some reason. ( and if he " must" he'll have to practice!)
What does he want to do in all of this?