Two of my classmates, which I will not name, apparently play their 3DS during class when the teacher isn't looking. I didn't tell the teacher 'cuz I'm not a tattle tale. You wanna know the funniest part? One of them had his 3ds WITH THE SOUND ON. And the teacher still never found out. These guys lucked out. Huh, I wonder if I can do that...Yeah, like I'm even gonna try.
TL;DR: Go ahead, kids! Play your game systems in class!