Big John is a mountain of a man. He used to be a professional footballer, at the height of his career playing for first division Wimbledon in the days of Vinnie Jones and the Crazy Gang, 20-odd years ago. He is not a man you mess with.
Whenever I meet him in the school reception, I feel like a cowering Year 7 boy beneath his bulky height. I find myself pulling back my shoulders in an effort not to look the weed that I am. Big John is cool. I am never allowed just to shake hands with him, but have to do his complicated hand grip and high-five routine. I always get it wrong. It's like having to do cheek-kissing rituals with middle class ladies who admire the French: I always end up kissing their nose by mistake. Fortunately, I have not done that with John, but you get the idea of the cultural gap.
That is why we employ John as a mentor for some of our more reluctant pupils. He is everything that they are not: city, not country; black, not white; mature, not still struggling to find a role in the world. He had a tough childhood in inner-city Birmingham; his dad was in prison. We hope that our kids will be inspired by the stories of a man who put disadvantage behind him to attain success.
We use him to work with a group of pupils who have not listened to the rest of us. They respond to the respect that he quickly earns and to the unsettling effect of someone from a very different world and experience than theirs.
I have no doubt that his mentor group of likely lads and girls are little kittens compared with the streetwise kids in some city schools, but they see themselves as top dogs in the Kingsbridge underworld.
They are the ones strutting their stuff on the town on Saturday nights; the ones who bring the weekend's troubles into school with them on Monday mornings. They are the ones with terminally short-term vision, concerned more with where to steal enough for their next packet of baccy and drugs fix than with passing exams or what job they might do.
John decided that a trip outside their own small backyard might help to bring a new perspective and show them that they were not as far up the pecking order of the world as they thought. So he drove four of them over the cattle grid on the Devon border to visit some of the kids he mentors in Birmingham.
It all sounds like one of those reality television shows: yokels with dung on their wellies clash pitchforks with sassy streetwise gang members tooled up with blades and trainers, innit?
The two groups did indeed approach one another warily. They complained that neither could understand a word that the other group was saying. Once John began to translate, some kind of communication clearly took place because a remarkable event occurred on their return.
One of our boys, Badger, asked if he could deliver an assembly about the trip. This was a boy who had either skipped or slept through every assembly of his school career.
He prepared all the PowerPoint slides himself and turned up on the Monday morning with his mum: she was so proud of what he was doing that she wanted to be there too.
Badger treated us to the tale of his life so far. He described his attitude as being "too cool for skool", accurately portraying his disruption of lessons, his rudeness, defiance, smoking, drinking and fighting.
He talked of all the attempts that had been made to turn him around, including talks with five counsellors, two mentors, a drug counsellor, spells at a pupil referral unit and, of course, Big John. He analysed why none of this had helped, saying that he did not want to listen, that he was stubborn and had no trust in adults - until he met Big John.
He spoke with awe of the young people he had met in Birmingham. He could go anywhere in Kingsbridge, but for them there are some streets they just could not go down or they would be dead - literally, a knife in their guts.
He told us that these guys don't do drugs because they had to be fit to defend themselves. He paused for dramatic effect: they treat their body like a temple. They don't waste themselves like we do in Kingsbridge, he said.
He was putting his disruptive past behind him and advised the year group to do the same.
The audience was suitably impressed. One Year 9 girl came out of the assembly saying she nearly cried at the transformation that Badger had undergone and the honesty with which he described his conversion.
We don't do hallelujahs in Devon, but this time we were close.
At break time, Badger was caught smoking and ended up in detention again. We had to laugh. You can't win 'em all: but it doesn't stop a single teacher in the country trying.
Roger Pope, Principal of Kingsbridge Community College, Devon.