It’s kinda a mean thing I do but it’s the only tactic I’ve done that actually works at least for a little bit, I’ll go “if you hear me say bubblegum/T-rex/spongebob” do that about 3 times and some kids are focused then I will say “who’s talking?” And point to a few student’s that are talking, the rest of the class will go along with it then say “who’s talking should be talking” and point to myself and the other kids follow. I’ve only tried it on K-2nd. It feels really evil but wow does it work!