BTDT - library story time groups, science classes, lego classes.. you name it and we've had these issues.
I agree that they worry more about the social aspect of it all - they are concerned about keeping kids in their seats long enough to focus on the activities.
And I agree with Portia - it's one thing for your child to enjoy the class, but rarely will the older kids appreciate, much less enjoy, being shown up by a child so much younger than they are.
Should this be your concern? not really - and if it were homeschooled/unschooled kids it would not even be an issue.
But it will be an issue if they do any group work - for your son.
Aiden started cubs a few months early, and now nearly 8 months in is STILL getting flack from some of the kids (and very subtly some parents) about his age, and his ability levels. There are always comments about his "Grade" level too - every single week my kid has to justify why he is working across grades 3, 4 and 5 but is one of the youngest there. Esp when he corrects reading/spelling/maths by older kids.
It's not fair but it is what happens.
Perhaps you could offer to host a similar program for mixed age high ability mathy kids?
