I don't know what the situation is for tablets, but I used to teach computers. The best solution was to know the technology better than the kids. After a few weeks, they realized that I had a "telepathic" ability to detect when they where goofing off and most of them gave up trying. The telepathy was little more than recognizing visual cues, some of which were on screen and some of which were in their posture. (Either way, it's a lot easier to detect than the visual cues of goofing off in non-technology classrooms.)