I think it's great he has caught the fire and you are encouraging and working with him early on! I've always been a believer that anything you learn early in life becomes more engrained in your brain and or muscle memory whether instrumental music, golf, skiing, etc. and thus more enjoyable later in life. I remember learning how to ski and going many times as a kid and now I can "just ski" without the negatives of overthinking it. For me, golf is the opposite. Never learned nor played until maybe 28 years old and it remains a torturous experience despite reading about technique, watching videos, etc. Just my opinion, but I would totally drop the idea of having a middle schooler (and or you) lug the school tuba back and forth. That will get old (or dented on the bus) real quick! Rather than paying to fix the wheels on the case if he seems to really be interested, which is outstanding, I'd be thinking of acquiring a tuba to keep at home. This ideally would be inexpensive, yet not so that it would hold him back in his development. TubeNet is a great source for finding such a Tuba once you have determined the make, model, and key of his school Tuba. Good on you -- this world would be a better place with more TubaMoms!
Bob Tampa FL USA
Euph -- 1984 B&H Round Stamp Sovereign 967 / 1978 Besson NS 767 / Early 90s Sterling MP: 4AL and GW Carbonaria
Tuba -- 2014 Wisemann 900 CC / 2013 Mack 410 MP: Blokepiece Symphony American Shank and 33.2 #2 Rim