In terms of career changes, English teacher to sharedealer must be one of the more extreme shifts. Especially when the teacher says he didn’t know what a share was, was useless at maths and knew nothing about finance.

But Alexander Davidson made the break, and now writes books about how to invest money. His latest, Everyone’s Guide to Online Stock Market Investing (pound;16.99), is published this month by Kogan Page.

What prompted this move? Money, he says. Or the lack of it. As a 27-year-old teaching at Chatham grammar school in the late 1980s, he says he was “working very hard for little money, I had no savings and couldn’t afford a house - I realised that something was wrong”. Seeking an easier way to earn a living, he decided to try his hand alongside the wheelers and dealers in the City. And having found a job where he could train as a sharedealer, his income rose to six times his teacher’s salary within four months.

How did sharedealing compare with teaching? “Teachers work much harder, are more skilled and more responsible. The staffroom was full of well-educated, cautious, dedicated people. But they were also naive and had no understanding of money - in retrospect, I was even more naive than most of them.”

Among the sharedealers, he found that he was working alongside people who were hardly older than the pupils he’d been teaching. “And they were opportunists, not necessarily well educated. The biggest difference was they were motivated by money.”

Although the financial world has a reputation for being an all-hours profession, he says that, in practice, the classroom was more stressful. “In the City, there is nothing to compare with marking books until 11 o’clock every night.”

Once he’d learned about sharedealing, he says, it was a considerably easier way of earning a living. And you have to wonder about the values of a society in which a sharedealer making a 10-minute phone call each day can earn more than a headteacher responsible for hundreds of young lives.

He says teaching helped him to develop an aptitude for research and absorbing information quickly - teachers, more than most other professionals, have the kind of knowledge-gathering skills that are needed by successful investors. But they need an extra ingredient to add to their analytical skills - risk taking. Something, he says, he found he had a flair for. If teachers are considering investing, Davidson advises them not to be intimidated by jargon. “There are lots of bluffers in the City - it’s important to be cynical about any advice you’re given, to get behind the smokescreen.”

His book looks at buying shares online; he says the internet has been a huge breakthrough for private investors. As well as making the buying process simpler, it provides masses of information. Anyone wanting to invest should research the companies and industries in which they want to buy shares, he says. And the target should not be to follow the most popular, but find under-valued shares that are likely to increase over the long term.

The book provides an introduction to investing on the stock market, suggesting when it’s the right time to buy or sell shares, and how to develop an investment strategy. “It’s the book I wish I’d had when I started out,” he says.

s.coughlan@virgin.net