During term-time 17 per cent of 14 to 15-year-olds are in paid work for more than 10 hours each week, with 5 per cent working more than 15 hours per week, and 2 per cent more than 20 hours.
When these are added to homework and school time, many teenagers easily top 48 hours a week - the maximum for adults under European Union law.
The research, by the Further Education Development Agency, also found that 65 per cent of 16- to 19-year-olds work for more than 10 hours each week, 22 per cent work for more than 15 hours, and 11 per cent more than 20. These teenagers study, on average, around 36 hours per week.
The survey also shows that the majority of teenagers are being paid above pound;3 an hour - the minimum wage for 18 to 20-year-olds.
Chris Hughes, the agency's chief executive, said: "Working is part of the reality of teenagers'
everyday lives. Putting a stop to it would be difficult and not necessarily desirable.
"Instead, we need to find ways of limiting teenagers' working hours if they are not to be early victims of the long-hours culture."