One in three adults in the UK regrets not having got better qualifications while at school, a Learning and Skills Council (LSC) survey has suggested.
Adults who had retrained said their employability was enhanced
The survey of more than 2,000 adults also found 27% regretted not making the most of the opportunities at school.
More than a quarter (28%) said they did not work hard enough while they were at school and felt they were now living with the consequences.
The poll found 35% had opted to go back to college to get more qualifications.
And more than one in four (30%) of those who had completed retraining said it had made them more employable and 17% had got a pay rise.
More than a quarter (26%) said their job was more rewarding as a result of retraining.
Julia Dowd, from the LSC, said: "Unfortunately, in today's competitive world, it's highly unusual for people to follow the likes of Alan Sugar and Richard Branson and achieve great success without any qualifications.
"Now, the best chance anyone can have is to achieve at least five good GCSEs, or a Level 2 diploma.
"So today, we are calling on all young people to ensure they achieve at least the minimum set of qualifications before leaving college or school, which will increase their employability."
Skills Minister Phil Hope said: "With 20% of adults saying they did not realise how their choices at school and college would impact their career options, this research underlines the importance for young people still in learning to think hard about their future as the decisions they make will affect the rest of their lives.
"Our message is that whatever your background or talents there will be a learning option for you. It may be an apprenticeship or work-based learning route at a college.
"The quality, status and relevance of vocational qualifications have never been higher and these days they can set young people on their way to foundation degrees, higher education and top careers.
"Colleges are becoming highly focused on employers' needs so training has to be practical and high quality, combining the theory and practical skills people really need."
On Thursday, Chancellor Gordon Brown said firms must meet their responsibilities to train their staff.
He said workers had to be offered second and third chances to develop the right skills if Britain was to compete in the world.
But while some firms worked hard to make that happen, many others were "too short-termist or take short cuts or don't believe that they should contribute".
But shadow education secretary, David Willetts, said Mr Brown was telling employers to make up for the failure of his government's education system.
"Gordon Brown is right to be worried about skills levels in Britain," he said.
"After 10 years in government, more than 20,000 children still leave school without a single GCSE and fewer than 50% achieve five good GCSEs including English and maths."