My dd9 is very into sports - she has a particular sport that is her passion, she participates in a few others that she also loves, and any new sport she's introduced to she automatically wants to join a team/group and add yet another sport into her already over-crowded schedule. We've let her follow her heart with her sports outside of school simply because being able to fuel that passion also fuels her 24/7 in other ways too - it keeps her happy
The one thing it doesn't do is take over her mind to the extent that if she's bored in school she daydreams about sports, and it hasn't replaced any of her drive to excel in her academics. If she's bored in school, I still hear about it
If you have doubts about whether or not your ds is being properly challenged in school, I'd ask him about it and also check in with his teacher. Go with your gut feeling on it - you probably have a good idea of what's up
Best wishes,
polarbear
