Unfortunately, most of us have all had "that teammate/group of teammates" & it does make a difference when it comes to team mentality. Kids are going to try and live up to expectations of them. If the bar is being set at "sometimes come to practice. sometimes go to class. I don't expect you to practice at home", that is what kids & their parents are going to go off of. If the bar is set as " you must be at every practice unless it is ___listed reason in tryout constitution (there will be enforced consequences). you better practice at home or i will be able to tell & I will pull your tumbling pass/stunt/etc if I don't see you putting in effort. If you don't go to class you will fall behind the other dedicated kids & let down your teammates who are trusting in you to give your all.", the motivation to succeed as a team is vastly different. That's not to say that every kid will have the same internal motivation, but there is at least a precedence of consequences for missing practices/not putting in effort, which could be an external motivator for a few that wouldn't push to better themselves on their own. ("i can't wait to go to practice!" vs. "i should go to practice because if I don't, the coaches will move my spot to the back)
So I guess in summary, there is no magic pixie dust to make every kid care & work hard in this sport, BUT you want to be at a gym where the expectation is there. If the gym/coaches don't take crap from kids/parents when it comes to excessive absences, low work ethic, etc. then there is at least a clear expectation to go off of. These are the gyms that are successful in the long run.....they don't try to be the "cool gym". They are clear in what they ask, consistent in their teachings & discipline, and they know when its time to work vs. play.