Many were also competitive at sport, were an only child, or had no formal educational qualifications, the Living Business Survey 2005 by the Royal Bank of Scotland found.
Overall, it discovered that 84 per cent of Scots currently running their own business had worked to earn extra cash when they were still at school, matching entrepreneurs like Kwik-Fit founder Sir Tom Farmer, who cleaned cookers and sold milk before quitting school at 14, eventually building a 1 billion business empire.
RBS said: "The drive to earn money and be self-sufficient starts early within the Scottish small business community."
Most popular earners were delivering papers (30 per cent), family business (24 per cent) and shop or restaurant work (20 per cent). Most Scottish business owners left school at 16, although most started working at either 13 or 14.
Steve Richards, head of RBS Business Marketing, said the study aimed to identify key factors from entrepreneurs' formative years to discover their characteristics and drivers.
The poll of 615 businesses found that 40 per cent of founders were either the youngest or a younger child. But women entrepreneurs were more likely to have been the eldest child (37 per cent).
While the survey focused on small business owners, many would no doubt hope to one day emulate Dunfermline-born Andrew Carnegie, the former cotton mill bobbin boy who left school at 13, went on to build the Carnegie Steel Company and become America's richest man before selling his company to JP Morgan in 1900 for 270 million - worth around 19bn in today's money.
RBS found that being competitive at sports was the characteristic that owners of small businesses were most likely (46 per cent) to have believed they displayed whilst young, with 51 per cent of men and 30 per cent of women citing sport as a driver.
That can be seen in David Murray's metals, property and football business Murray International Holdings, and Cairn Energy, the FTSE-100 oil business built by former Scotland rugby international Bill Gammell.
"There appears some correlation between early competitive spirit and later business success," Mr Richards says.
The report shows educational attainment among Scotland's entrepreneurs was varied, but despite their later successes, 45 per cent of owners of small businesses rejected higher or further education and left school at 15 or 16. Nineteen per cent had no qualifications; 29 per cent achieved some Standard grades; nine per cent secured Highers.
However, around 12 per cent held university degrees in a similar vein to Sports Division founder Sir Tom Hunter, who worked in his father's grocery shop while at school before attaining seven Highers and a marketing and economics degree.
Mr Richards added the study showed Scottish entrepreneurs "believed energy and determination were equally the most important characteristics to contribute to business success".