Silence is golden is a classroom mantra repeated the world over.
But, imagine a classroom being shaken by a sound louder than a rock concert; a sound as loud as a thunderclap or a chainsaw.
Welcome to the classroom of Annalisa Flanagan - the owner of the world's loudest shout.
The Belfast primary school teacher bellowed her way into the world record books in 1994 with a thunderous bellow of the word (what else?) 'quiet!'.
The shout clocked up an earth-shattering 121.7 decibels, setting a world record and potentially damaging the hearing of anyone within earshot.
Despite her record standing for 22 years, no-one has yet been able to out-shout her - a fact that recently re-emerged when her Richter-scale rippling exploits featured on the hit BBC TV programme QI.
Corey Taylor, lead singer of renowned heavy metal outfit Slipknot was on the show - and even he was blown away.
"Our shows top out at 109 (decibels) and those are quite loud," he said. "So 121 is stupid."
Fortunately, even though Annalisa has this sonic secret weapon to unleash on her pupils at Finaghy Primary School, she insists it is one she never uses.
"I'm really not a shouter," she laughed. "I'd much rather bribe the kids with sweets than shout. I want them to love me!
"Also, after the first couple of weeks of teaching you can't be shouting all year. I'm hoarse all the time as it is."
Her pupils back her up too, and appear to be sincere when they say Ms Flanagan mostly keeps her hidden talent for hollering outside the classroom.
In fact, her skill is completely unrelated to teaching and purely a coincidence.
Indeed, the gift is one that probably would have stayed hidden, if it were not for a streak of competitiveness.
"In 1992, I was at a church summer camp. There were about 500 people attending and they held a record breaking day," she recalled.
"Now, normally I'm quite a competitive person. They had this shouting competition, but to be honest, I thought it was a bit embarrassing so I stayed out of it.
"But, then one of the kids told me my twin sister was winning. So I thought, if she is good then I'll be good too."
The competition was taking place in world record conditions, meaning whatever was recorded was eligible to smash the old record of 119 decibels.
"My sister got 119.1 and I got 119.4 - so she held the record for a little while, and then it was me."
Two years later, Annalisa was invited to defend her title at an event in Belfast.
"I got 121.7 decibels - and it has stood ever since."
Annalisa said she was amazed that her almost-accidental record has endured for 22 years.
Even though she admitted that she would be considered on the loud side, the teacher said she had no particular technique.
"I just open my mouth and let rip," she said. "I was on a TV programme and they took me to the Harley Street Clinic, where a lot of singers would go to get their vocals checked.
"In the end, the expert's conclusion was that I was so competitive when I set the record, so determined to beat my sister, that it spurred me on."
However, it is an ability that has diminished slightly over the years particularly after her tonsils were removed.
"I don't like being measured as much any more, because I'm nervous I won't really get to be as loud," she said.
"I can get to around 115 but I haven't come near 120 in a while. It's difficult to match the record. I'm not sure if I'm holding back a little bit. Also it hurts my head when I'm on full power."
Meanwhile, the children she teaches remain suitably impressed by their record-breaking teacher.
"It's quite sweet actually," Annalisa said.
"Sometimes I see past pupils who are in their 20s walking past the school gates. They would go: 'Alright Miss, still the world record holder?'
"It's just mad that it (the record) has stuck this long."