Some appear at your door in their late teens. They'll tell you proudly that they're training or studying at college. They remember their primary school with pleasure and want you to know they are doing well. It's gratifying, and occasionally surprising, especially when a youngster visits who spent most of his primary years being a thorough pain in the neck.
Rhamid was such a child. He was in his final year when I joined the school as headteacher, and I learned that he'd been very difficult in Y5. I was warned that I'd probably have to exclude him in his final year.
Undoubtedly, he could be charming. He was the first child I encountered when I arrived at Comber Grove, since he was the first to arrive in the playground each morning. He offered to carry my bags upstairs, and when we reached my office his eyes darted quickly around the room. I had the impression, even then, that half an hour later he could have drawn me an accurate map of everything it contained.
Within days I discovered that nothing was safe when he was in the vicinity unless it was nailed down, but catching him was impossible. I also found that he could irritate his classmates with consummate skill, causing arguments that degenerated into utter chaos - at which point, like MacCavity, Rhamid wasn't there.
But we had to get through the year and I suggested giving him a main part in my Christmas play. This occupied him for several hours a week, to his teacher's delight, but gave me undeniable grief instead. Rhamid constantly rewrote his part, demanding that other cast members keep up with his changes and gave them a tongue-lashing if they didn't.
He would take himself off to the stockroom and use copious amounts of expensive card to create intricate props he'd designed. He would persuade teaching assistants that I had said he could stay in at lunchtime to practise, and chocolate bars would suddenly disappear from lunchboxes.
Ultimately, the cast rebelled and said they didn't want to be in the play until I'd sorted Rhamid out.
Then, at hometime one freezing winter day, my car keys disappeared. I'd left them on my table while I fetched my coat and I searched everywhere, until a cleaner said she'd seen Rhamid go into my room. I rushed downstairs and caught him by the door, asking if he'd seen my keys.
He looked surprised and hurt, offering to turn out his pockets. Two weeks later, he put his head round my door, grinned and jingled a bunch of car keys. "Are these yours, sir?" he asked innocently. "I found them in the road."
Shortly afterwards, Rhamid was sent to the library to work. A special needs group was also in the room, reading with a teacher. At lunchtime, the teacher popped out to the shop and realised her credit cards were missing from her bag.
This time I told Rhamid I'd have to search him, but he raised no objection, merely expressing his sympathy for the teacher's loss and offering to help look.
Somehow, we reached the end of the year and Rhamid moved on. Then, seven years later, a smart young man appeared in the corridor. It was Rhamid, and he wanted me to know how well he was doing. He'd almost finished his business studies and was going into partnership with a friend. Pleased to know things were going well, I invited him to say hello to the teachers he knew.
Four years later, he appeared again, in a smart suit and carrying a very expensive briefcase. His business was successful, he was marrying soon and he hoped he could put his children in our school as it had given him such a good start in life. Once again, I expressed pleasure at how things had turned out.
Until, reading an evening paper a year later, I stopped at a picture of a young man who was wanted for a string of daring robberies in one of London's smartest districts. Always immaculately dressed, said the headline, and carrying an expensive briefcase.
Mike Kent is headteacher of Comber Grove primary school in Camberwell, south London