The nature of the sexual cycle is arousal leading to orgasm, plateau and resolution.  If this cycle occurs for you so rapidly in class and you ejaculate semen, despite your focus on the work of ballet, you need a medical evaluation.

If, on the other hand, your problem is leaking seminal fluid (see above), the approach may be different.

I'm not denying or denegrating your post.  There's an old saying in Medicine: "If you hear hoof-beats, expect horses, not zebras."  I know that rare events occur ("zebras"), that's why I think you should talk to a physician.  On the other hand, common occurrences should be thought of first.  Unfortunately, on this (and some other boards), a common event is a confabulation.

If you have this problem, get checked out.

DancingDoc