Not sure what the reason is but DS7, very vs, does much better with individual lessons for physical stuff. I'd say that it's mostly because he is always cautious and often anxious, and needs a lot of encouragement and repetition. So we do things like shell out for an hours individual skiing lesson on the first day, which cost as much as a days group instruction, but he'll learn tons more, then have him in group classes the following days, for the company.
Swim class with a lot of individual attention, due to kids entering and leaving at various dates, worked much better than the following class where everyone. Was supposed to progress at the same level and speed - he just didn't, regressed in fact. So we switched to yet a different class, and if that hadn't worked out, I would have booked a few individual lessons for him.
Yes it's costly, but the group lessons that had him do worse in the end were such a waste of money.
