When I go to ballet class, I believe that it is important to be dressed appropriately. But not all girls are. This can be a distraction to you as a dancer, and sometimes the teacher because they might not be able to see your correct posture and technique clearly. At dance.about.com, I found this:

A simple leotard and a pair of tights is the best thing to wear to class. Leotards are available in several colors and designs, including sleeveless, short sleeved and long sleeved. Young dancers delight in wearing small skirts and tutus over their leotards, but most teachers discourage them in older classes.”
Is this what you usually wear to class? Do you believe that it is important to dress appropriately? Does your ballet teacher have a strict dress code on what you should wear?