Wow! Sorry, can’t believe I just saw this!! Our series is all about working with teens so I feel your pain. Luckily for us, our teens are almost all insanely well behaved on set. Even so, everyone gets stir crazy after awhile and focus can spiral downhill fast.
For us, I find by the time “sound speed” is called and “camera rolling” the majority are quiet and back to focusing. However that’s not always the case on a set with a large amount of extras. I found when we filmed our big classroom scenes or high school party scenes the easiest way to get people to focus was a nice but firm, “Alright guys, let’s focus and get through this thing!” did the trick. Not getting angry, but reminding them that the sooner we focus, the sooner we move on is our best bet most of the time.
With our teens we make sure they have ample breaks for snacks getting a little chatting out of the way. While they are professionals, they’re also still kids which can be easy to get and is important to keep in mind. I often find taking a moment to make sure they’re well hydrated and fed goes a long way. This is true of adults and teens alike, tbh.
As far as working with your peers goes and having them take you seriously, I think being very clear from the beginning is important. If all that fails, @HackettKate said it best with the “I’m waiting on YOU” face. lol