I always take my tama to school. And if the teacher is a push over. Play it when she is not look ing. If she/he is strick, play it when they leave the room or put it on pause
Put the sound off! you can kind of not be noticed at all by doing that.... Try to hold it under youre desk, in a way that you can still see the screen. It works for me! I do it all the time! Also, take the advice from the message above mine, those are also good hints.