This morning I have read somewhere in the Web a possible warmer for kids at the beginning of classes.
She, the teacher who wrote about this, said that she has a class just after lunch, so the kids arrive so playful.
She advises to play a song that be energetic, and as a second step she would play low volume songs or chants.
I think and I have seen it, a teacher that used to play a CD of classical music at some specific time, while the students had got to write some exercises or essays (compositions). / Photo from: violin-posture www get-tuned com