KEEP IT DOWN! = stop being so loud (very common)
👉🏻 Why won't the neighbours keep it down? Five times an hour! Ridiculous!
👉🏻 Keep it down, won't you? (Q.Tag adds more stress as if I am in a library or people are really irritating me)
PIPE DOWN! = slightly politer form of shut up (common, informal)
👉🏻 Oh for heaven's sake! Would you just pipe down for a minute?
👉🏻 Oh pipe down, would you? I've had it up to here!
QUIETEN/QUIET DOWN = stop being so loud (common, formal-ish)
👉🏻 Come on, guys! Quieten down, please! The lesson has started!
👉🏻 Can you quieten down the dog somehow? Feed it the cat!
SETTLE DOWN = be quieter less active (common, semi-formal)
👉🏻 Come on, kids! Settle down and get your books out!
👉🏻 Yeah yeah, settle down everyone! Funny joke that was!
❗ CALM DOWN would work as a synonym here.
There are many ways to say: Don't speak but I will give you ones that you can us in the classroom that aren't rude or aren't soooooo rude.
GIVE IT A REST! = stop talking. IT - mouth/tongue
👉🏻 You two at the back - come on, give it a rest!
SHUSH! = silence (but you must put your finger in front of your lip when you say that)
HUSH! = exactly the same as SHUSH
ZIP IT = keep your mouth closed (Not so rude but maybe a little bit harsh)
👉🏻 Oi, you two at the back, zip it! Last warning!
❗BUTTON IT would work as a slightly politer synonym here
CAREFUL: I have heard a couple of teachers use: Bite your tongue when saying quieten down. That's not correct. BITE YOUR TONGUE = forcing yourself to keep your mouth shut because you really want to say something.
👉🏻Yes, I know that student says the stupidest of things. You just have to bite your tongue and not respond!