Attendees in Lobby Hearing Each Other while waiting

tdwachur Hello, when being stuck in the lobby there's nothing more to it than wait to be admitted. If you're not being admitted you will be dropped from the lobby (the official docs says 15 min, but I've heard someone in the community actually testing this saying 30 min). Anyway, you cannot hear or communicate while in the lobby. That's one of the main purpose.

If I should guess though, your org. hasn't really worked through all the available policies in Teams so perhaps the students are creating meetings on the side, calls and chatting as there are no boundaries set up.

I would like to recommend this article for configuring "safe learning" and note the tabs!
For administrators - For educators - Policy quick guide

Keeping students safe while using Teams for distance learning (microsoft.com)