There's a strict no-running rule at Motherwell's Braidhurst High, but one person is allowed to break it.
David Gardiner, PE teacher and principal of pupil support, whizzes around corridors and bounds up stairs three at a time. Running is a natural instinct in him, and a passion that inspires pupils. What, asks headteacher Derrick Hannan, would be the point in suppressing that?
Mr Gardiner is an accomplished long-distance runner whose latest challenge is beyond the comprehension of most: the 100K ultra-marathon, a 62-mile race that makes standard marathons (26 miles) seem puny.
He ran his first in May, a punishing trudge around Cardiff lasting 8 hours and 42 minutes, during which he became dehydrated after 40 miles, having failed to eat and drink enough. He learned from those mistakes for his second event in Perth, however, and finished in 7 hours 36 minutes. That got him into the Scottish Commonwealth team. Although not a part of the quadrennial games, an inaugural ultra-marathon event will be held for Commonwealth nations in Cumbria next September.
Mr Gardiner is modest and quietly spoken, but others will tell you that his achievements have a big impact on pupils - once they work out just exactly how far he goes. "The marathon they can just about get their head around - they've seen it on the telly," he said.
He has tried explaining that the ultra-marathon is like running from Motherwell to Perth, before realising that this meant nothing to pupils whose sense of geography struggles to reach Coatbridge, eight miles away. The penny finally drops, along with a roomful of jaws, when he tells them to think how far you could drive in an hour, then imagine running the same distance.
The first hour of the race is about finding a groove and hitting your target pace: Mr Gardiner's mistakes in his debut meant lap times oscillated wildly between 14 and 28 minutes. The second hour is comfortable and "a bit boring", a feeling not alleviated in Cardiff where competitors had to complete the same circuit 42 times. Thereafter, "you just start getting into the race".
It is in the last two hours that the body protests: "You're hanging on for dear life, concentrating on putting one foot in front of the other," he says.
Fuel constantly needs to be replenished: a drink every 15 minutes; a sports drink every hour; some potatoes and a banana every two hours. Towards the end, as mind and body become addled, flat Coke and Mars bars provide instant sugar hits.
Despite the huge mental and physical drain, Mr Gardiner thinks little of turning up at school the next day. Mr Hannan, a keen runner himself, is amazed at his colleague's power of recovery. "He'll just say, 'I'm a wee bit stiff'."
Mr Gardiner's example has encouraged a stream of proteges in a school with only 570 pupils. S4's Craig Wellcot, a similarly unassuming character whose confidence grew as a natural talent for running flourished, won the World Youth Games 1500 metres in San Francisco. Chelcie Dalziel, also S4, is one of the top sprinters for her age in Scotland.
"We've found that young people are following in his footsteps and getting Scottish vests - representing not just their school or authority, but Scotland," Mr Hannan says. "I'm convinced that without that role model, they wouldn't have got to the stage they're at."
At assemblies, Mr Gardiner's example appeals not just to budding sports stars. He recalls that no one would have marked out his retiring 14-year-old self as a teacher, but success at running gave him the confidence to do well elsewhere.
He explains that the daunting ultra-marathon is not to be feared: "It's difficult - that's why I enjoy it."
He runs 120 miles a week for the sheer enjoyment and sense of peace it provides, and encourages pupils to find their own passion, whatever it is, and see where it takes them.
Challenges remain for Mr Gardiner, who, at 39, is in peak condition for ultra-marathons since most top competitors are in their late 30s or early 40s. He insists that the really tough runners compete in 24-hour events and cover 150 miles. That's Motherwell to Aberdeen - or three hours in the car.