Some teachers start the class on automatic quiet. Students get
printed instructions,.or the instructions are on the board, and they
are asked to get busy - not noisy. Some teachers use a beginning
ritual waiting for them to begin working on. The teacher
instructions start after they are settled and working. This site has
more information.
http://www.goshen.edu/art/ed/ritual.html
I know one art teacher that uses as red flashing strobe to alert the
class that he needs them quiet.
Marvin Bartel