I am an academic and, over the course of my career/life, have come to the conclusion that academics is overrated. This is not to say that it is not important to take school seriously, and I agree that if a child is really struggling (as in close to failing a lot of the time), something needs to happen and gymnastics (or any other hobby, this isn't really a gym thing), needs to possibly scaled down, but this should only happen when really necessary. There is nothing wrong with being average, and whether or not you remembered the year of a certain battle in your history quiz is completely irrelevant to the rest of your life. I realise this is maybe simplistic for people living in countries where so much rides on school performance (I was lucky enough to grow up in a country where, as long as I passed my final exams, I was free to go to any of the (equivalent) universities to study pretty much anything - only things like biochemistry and medicine with very limited lab spaces had any entrance restrictions), but I don't believe putting academic pressure onto young children translates into more qualified adults. Instill a love of learning and those sufficiently academically gifted will do well, while those less academically gifted can follow their love of learning in a whole host of incredibly important, but less academic, careers (certainly, where I live, I wish there were more plumbers, electricians, etc - all jobs that, even though it pains me to say it, are far more important to society than anything I do in my research). I wish those careers had the same prestige as the more academic ones. I think this would prevent many students from feeling like failures and create a happier society.
Okay, this has gone a bit off topic, but I truly believe that while leaving gym early to finish a school project should be completely acceptable and not be questioned by coaches, the standards of commitment and striving applied to children (you have to work hard for school and do you absolute best there - you cannot miss gym because you are committed to team) have gone beyond the realm of anything even remotely reasonable. Work ethic is important, but expecting unrelenting work ethic in a 10year-old is crazy in my mind.
I grew up going to school (half-day in my country of birth), doing absolutely no work for that outside (did my homework during lessons to save time - granted, being academically gifted made that easy, otherwise I would have had to put some more work in, I guess), went to gym three times a week (which I loved more than anything, but was very very mediocre at, which was a really good balance for me, since I had no expectations riding on my performance there!), played an instrument that until age 14 I hardly practised on at all (my mum insisted I keep going), and spent my remaining time reading (child/YA fiction, not anything educational) and roaming the fields near where I lived. I still grew up into a responsible adult with a research career who, for the most part, manages to get on with things (not so great on household chores, but...). I am very happy that my childhood was not driven by the maxim to work hard at all times.