I wear alot of spandex type of gear and there are a couple of options that you could consider. One is try not think about it and focus on the dancing. If it does happen during the dance class, the more you think about it, the longer it takes to go away. The second option is abit more preventative. I say this with all seriousness. I find if you release yourself just before a public outting, there is much less likely of an erection for the following few hours. Basically I am suggesting that you masterbate about 10 minutes before you get changed into your gear(before you leave for your class), or before a recital. Your stress level decreases, and it is easier to concentrate on your practice. Your body seems to have started puberty(I am guessing), and this is one way to help control surprise pop-up visits from down under.
Hope this helps
Jared
>I've been dancing since I was 7 but recently my body has been going through changes and I don't seem to be able to put on a dancebelt and tights without getting an involuntary erection.>I'm worried that this might happen in the middle of a lesson, particularly during partnering class.[/i]