Quiet Down

There are many, many ways of quieting down a group of people. The worst one of all is to yell "BE QUIET PLEASE!!!" (But even that works once in a while.)

tips for teachers on how to quiet down a classroom

Walk up to the lecturn and extend your arms toward the audience palms outwards. Hold the position. It usually works.

In a smaller, more rowdy group (classrooms come to mind) walk in agressively, smack a large on the table, and shout I DEMAND PANDIMONIUM. This has a very high success rate, even if it does leave a few looking kind of confused.