Why hissing is good for you
But it is apparently what they should be doing if they want to protect their number one classroom asset - the voice.
A leading voice specialist warned teachers last week that they could be doing irreparable damage to their vocal chords as they battle each day with echoing classrooms, noisy children and bleeping computers.
Sonia Woolley, of the Voice Care Network UK, told a
gathering of Warwickshire heads that learning how to warm up and use the voice properly should be a key part of teacher training.
"The greatest tool teachers have is the way they communicate and the thing that does that is the voice," she said.
"You would never find an athlete competing without warming up properly but this is what teachers do on a dily basis.
"You can get away without using your voice properly for so long but there will come a time one day when you are shouting across the playground and it will suddenly go."
The good news is that it takes only a few simple steps to keep your voice box in perfect order.
Breathing correctly and maintaining good posture is essential - standing like a sergeant major with the chin raised to heaven will not result in optimum voice output, Ms Woolley advised.
She also recommends humming, hissing, tongue-twisters and deep breathing on the floor as essential ingredients of any successful warm-up, while focusing on the "three Ps" - power, pace and pitch.
Maxine Cherrill, head of Warwick nursery school, said: "My voice goes all croaky by the end of the day and it's the first thing to go when I'm under stress. It simply never gets a break."