Teachers in any kind of child, teen, adult education or college classes need their students to have basic good manners. Listening, not disrupting the class in any way, are skills that teachers hope every child has before they come to kindergarten. If only.
In ballet and dance classes progress depends on quick understanding by the students, as the physical doing and repetition of a correct movement is what creates good technique. And good technique is the basic ability, then talent, style and other aspects of presentation follow.
So what is a professional attitude that would help ballet and dance students who do not even have professional aspirations? Should they care?
Many inherent factors in the performing arts trainings can bring out the bad attitude in many of us, naturally. Some teachers are drawn to teach and correct to the physically gifted and more charismatic students, even if they are not good workers. This can raise the resentment of other students. I understand this. However, the professional attitude of everyone is to just keep working hard. It is also alright to ask your ballet teacher, at least every few weeks, "what should I be focusing on the most right now to improve?" If you have to demand attention, you do, in a polite way.
Of course if this is a real problem in your ballet studio, go somewhere else.
Casting for performance roles is naturally an issue. Everyone hopes that she or he is ready for the lead or solo roles, or realistically knows that they are not. On the management end, it is true that those teachers doing the casting sometimes do consider students whose families support the school, or who have financial influence. Occasionally it is painfully obvious.
However you get cast, fairly or not, rehearse and dance every role like it is the most important role in the ballet. Because it is. It is YOUR role. That doesn't mean you demand any extra attention with superfluous smiling or any other kind of exaggeration. Do not distract yourself with envy (though it is a natural reaction to feel it, keep it under control), grief, or moping. You can cry on the right shoulder away from the studio, but in the studio you act with quiet pride in all that you do.
You come prepared for every class and rehearsal. You do the minimal socializing, and do not join in the complaining committee of the other unhappily cast ballet students. Just go about your business.
If your ballet studio is presenting excerpts from classical choreography rent the ballets, different companies if possible, and see how the professional dancers do the parts you are rehearsing. Different dancers have different interpretations, musicality and style. You can always learn something to adapt in your way to improve your presentation.
A professional attitude is largely about self-containment. Get advice outside of the studio from family or friends, even other teachers. Release your emotional disappointment somewhere safe. But in the studio, just work. Be helpful to others when needed, as long as it doesn't take away from your work.
Get an edge on your competition as well by studying the expert dance manuals that are available. Improve on your own, take care of aches and pains, eat well and sleep well. Everyone respects that, whether they say so or not. Become your own expert and be a pro, whatever you do.