Class of 30 year 11 boys. About 6 lovely ones, 7 hardcore troublemakers and the rest hangers-on who won't instigate poor behaviour but will join in/escalate once it's started. Mostly I deal with it, but this week they've found a new game which is wang a paper ball across the room when I'm not looking. They're seriously quick - I don't turn my back on them, but I can just be looking at one student for a second and one of the others on the other side of the room pings one at someone. Cue loud comments of "did you see that,Miss - it was X", X loudly denies it and blames Y, etc. I know most of the time they deliberately blame the wrong person to get a reaction. It's so frustrating as they're too clever with it to get caught. What do I do? I've tried ignoring it, but that makes me look weak. I've bollocked them all, which works for a short time before they start again. I've kept the whole class in, but I only have them before break once a week - the rest of the time they have to get to their next lesson, and I don't like keeping the whole class back anyway. So what do you do when it's impossible to know who the perpetrator is (and it's clearly more than one anyway). Should add I only started at the school in January so I haven't had time to build much of a relationship with them.