This doesn't happen so much in daughter's gym. There are girls from 8-10 in her training groups and they all get on well but they just don't really have time to notice what is going on in other groups as they move around the gym. They chat to team mates when they arrive and are changing and, as all the classes are staggered start times and most kids travel, it is just their own team mates in the changing rooms. Then they're in the gym and working their socks off and pretty focused on their own group and coach, then they have a little chat at the end as they get their boots on and that's it!
It's not that they feel any different or seperate, they just don't have the opportunity to get to know each other. They would certainly acknowledge any girls from other groups if they saw them out of the gym, but that rarely, if ever, happens actually - they're all at different schools and have very different lives.
My son on the other hand, who spends quite a lot of time outside the gym waiting, has made friends with loads of kids from different groups. He plays with them as they wait for their class or wait for a sibling, remembers names names and looks forward to seeing them each week