You need two things...
One is a dancebelt. A dancebelt helps conceal this problem to some degree.
Two, is the realization that guys are human and have erections. You don't want to tape it up or tie it off, that can cause damage. You don't want to fold it down, because that makes it more obvious. Some of the people in your class may giggle, but being a human being is nothing to be ashamed of.
balletboy[/i]