My class still haven't figured it out. That when we are in full flow of a lesson, 'get out a pencil' does not actually mean 'start a conversation with your friend'. And that I don't expect them to start sniggering for no reason, call across the class or play with their desk lids while I am explaining to them what they are going to do. They don't get that, either.
So, every time it happens, I write the name of the perpetrator on the board, or put a tick against a name already there for repeat offenders. Three strikes - and they lose a chunk of playtime. Football time, actually, which is worse than just hanging around time.
Today they got the full teacher treatment. "This lesson will be more fun if I am having fun. And I am not having fun right now because I am too busy having to write these names down."
Shocked silence. They got it. For a while, anyway.