When the children are getting ready to leave the classroom, either for a different lesson or break time, I find it useful to sing a song as a sign that I am waiting for them to get into a straight and quiet line.

The song is sung in the tune of Frere Jaques:

Are we ready?
Are we ready?
Yes we are!
Yes we are!
Standing in a straight line,
Standing in a straight line.
Here we are!
Here we are!

You can exchange the 5&6 lines for 'Sitting in a circle', 'sitting up so nicely', 'listening very carefully', 'sitting very quietly' etc.

The children start to join in quietly as a sign that they are listening and I get very very quiet until I stop.

I also find with Form 3 that it often helps to stand with my hand in the air saying 'my hand is in the air' until all the children copy me and sit quietly, though it is very basic it gets their attention fast.