I am trying to find an American book that I read probably in the early 1980s but I think the book is older than that, probably from the 1970s. The book is about a young white girl (I want so say she is poor/), who is training to be a dancer (maybe a ballerina).
The girl gets impatient with her trainer’s methods, and he shows her that it is necessary to learn the fundamentals before she spreads her wings. He demonstrates by doing some sort of comic dance routine (or possibly mime), and then (I think) he does some sort of impressive, more traditional dance routine.
I think the girl develops a crush on some guy, and toward the end of the book, there is a dance, and she is feeling more confident. She has managed to find/make a candy green apple dress (possible matching purse and/or shoes).