Harry Ingram, 16, from Radlett, started selling stink bombs in the playground at Hertsmere Jewish Primary School, buying them for 50p and selling them for a pound. He also made a huge profit on sweets, buying them for 0.2p and selling them for 60p. He then set up two websites supplying practical joke items like fake parking tickets and whoopee cushions. And a website set up for his travel-themed barmitzvah, under the name of harryairways, proved an unexpected earner - he sold the domain name for £500 to another Harry who was actually setting up an airline. Nowadays he sources must-have electronic items, silver jewellery, and street wear, which he sources direct from factories in China, then sells them through his eBay shop and to his friends at University College School, in London.
"I'm the boy at school that people come up to and say, "I want these headphones, but I want to pay £8 not £80," and I can get them.
"Once I set up my websites, I got business from all over the country. Knowing that it wasn't just for my friends was a good feeling. At that time I got my own debit card and could stop borrowing from my parents. I made about £500 in a year, which is quite a lot when you're 11.
"Then I started selling phone accessories like cases, headphones and coloured trackballs (normally £40, but I managed to get them for 25p each), mp3 player leads and cigarette lighters. There are factories in China that will custom-make stuff for you.
"Most of last year was selling excess stock on eBay, where I have my own shop. I sell silver bracelets and high-end "lifestyle" clothing products, which I get direct from the factory in Cambodia. Last year I probably made about £1,500.
"I have also got involved in party planning. Earlier this year I made £3,600, planning an event with some friends in Hampstead, to which 600 people came.
"Having money to spend is good. I turned my bedroom into a club with lasers, a strobe machine and decks. But if I wasn't making money, I'd still do it, because I do get a lot of enjoyment out of it."
Harry has also turned his talents to raising around £5,000 for charity.
"When I'm 22, my CV is going to look quite impressive," he says. "My parents have given me a lot of support and my school promotes an independent streak in its pupils.
"I still want to go to university as I'll be more qualified. It's fine now to do these things to try to make money, but when I'm 30 I'll need the bank manager to take me seriously."