One of the dancers was Joan (Pronounced kho-an, not jone) Sebastian, a beautiful, elegant, stylish dancer, who was just 17 when the film was made. To dance like that at 17 ... !
This is a photo of him. So very beautiful.
And this is a video of him dancing while training for the competition. After the clapping, keep watching, there's a slowed down piece, where he shows how to do the final pirouette and élevé. See how elegantly and with what control and power he does it. I never achieved that mastery.