Wait for a break in your lesson or performance before you attend to your ripped tights. It's considered impolite to disrupt a ballet lesson so, although the matter seems pressing, hold out.
Keep the tights on and find the place where they have ripped. This method won't work if you take the tights off.
Spread a thin layer of clear nail polish over the tear in your tights to keep them from ripping further. Only one coat is necessary and it should dry in minutes.
Spray the nail polish covered area one time over with holding hair spray. A light coating will harden both the clear nail polish and the fabric of your tights so that the tights don't begin to unravel.