Hi! Haven't posted here in a while, but just wanted to share some of my personal experiences in playing a string instrument (violin) ^o^ .
It's great that your kid loves his instrument. When I first started playing in fifth grade, it was really difficult. Playing a string instrument as opposed to anything else is completely different. My fingers would hurt a lot of times from playing, and sometimes I couldn't get anything in tune. So it was like that, but my parents wouldn't let me quit despite my own wishes.
During sixth grade, I had a falling-out with my private teacher and for a while I was teacher-less again. Then came seventh grade, which was a completely different experience. I auditioned for my middle school's chamber orchestra, and surprisingly, made it!
That was the defining moment in my relatively short violin-playing career. The chamber orchestra in my school was made up of three grades together, and I was the youngest there. Nearly everyone was better than me and had played longer, so I was embarrassed to play in front of other people and always sat in the back. But my school conductor was amazing. We'd have after-school rehearsals as a club, perform in competitions, and even went to Hershey Park.
I found a new private teacher and started to enjoy playing the violin instead of it being a chore, and my playing improved a lot as a result. I built up enough confidence to play in front of other people, and to make mistakes in front of them too. There's always a lot of pressure, both school-wise and from your private teacher, but I've not regretted picking up the instrument and I'm glad I didn't quit back then.
One of the most fulfilling things about playing an instrument when you're young is the school-involved part of it, getting to see how other people play and learn from each other. It's great encouragement, and knowing how to function as part of a group within the orchestra matters as much, if not more, as your actual skill level. Playing an instrument also opens up a lot of opportunities - whether it be to go to competitions, play in a quartet with your friends, or just learn how to play that awesome piece you heard on the radio. I can only speak from personal experience, but stick with it if only for a little longer to see if quitting is really what he thinks is best.
I'm not too familiar with dysgraphia or how much it would affect playing an instrument like the viola, but it's said that higher strings such as violin and viola are arguably the hardest instruments to learn how to play well, and it does involve quite a lot of fine motor control. >_<
As a fellow string instrument player, it's not uncommon even after playing for several years to play on more than one string on accident, and playing in tune is always going to be a challenge, regardless of skill level. I would put myself as around an intermediate player, but sometimes during lessons I'd still play something out of tune, especially in the higher positions, and be unable to hear that the note isn't quite the way it should be until my teacher told me how awful it sounded. XD
And lastly - it's really not so much as how long you practice, but more the quality of your practicing and how focused you are. My teacher is alright - though admittedly not ecstatic - with my practicing twenty minutes a few nights each week, as long as I'm accomplishing something each time. As for being able to hear that the notes are in tune, some of it is natural ability (people with perfect pitch) and having a "good ear," but it can also be trained if you listen really hard while you're playing.
Sorry for the extra long post, but I hope I helped a bit. Best of luck to you and your son no matter where you decide to go with his instrument.
