This is
not my assumption!
I work in a preschool and one of the little girls does ballet at the weekends, as does her elder sister. Preschool girl is 3 years, elder sis is 7 years, so both pretty young, and their mum stays and watches the classes.
I was passing casual conversation with the mum and asked how the girls were getting on at ballet.
Oh, they are so fantastic and wonderfully talented dancers (hmm, the cynic in me thinks many parents think that about their children, whatever the hobby

). But if they weren't good at ballet, the mum wouldn't have them keep going. She just doesn't understand these mums who send their daughters to ballet when they're not good at it, why do they just keep going every week.
I managed to say politely 'Oh, I suppose it's good exercise and if they enjoy it, that's the important thing...', which got the clarification, she is not talking about children who do not appear to enjoy the classes but are there solely to fulfil maternal aspirations, she really thinks it should only be for those who are outstanding dancers. At 7 and 3 years.
My town has several ballet schools and I'm sure they're pretty reasonable schools, but we're hardly talking White Lodge here! (UK's Royal Ballet School's school
http://www.royal-ballet-school.org.uk/premises.php?s=3