Four in five people training to be teachers expect to be in the profession in five years' time, according to research.
Trainees in their twenties are less likely to be confident that they will stay in the profession than those coming to teaching later in life, a government-backed study found.
Student teachers on employment-based training were most likely to say they will remain in the profession.
Early results of the six-year Becoming a Teacher project based on a survey of 4,393 student teachers in England found that many had embarked on training despite misgivings.
Teacher morale and low salaries, each cited by one in five, were the factors most likely to deter trainees.
One in nine said they had been put off by the way TV programmes such as Grange Hill and Teachers portrayed the profession.
The study, funded jointly by the Department for Education and Skills, General Teaching Council and Teacher Training Agency, is the latest evidence that many young people no longer see teaching as a job for life.
Statistics show that one in three teachers leaves the profession within five years.
The study, which included students on a variety of training routes, found that older trainees were willing to make a greater commitment.
Only three-quarters of 20-24-year-old trainees said they expected to be in teaching in five years time, 6 per cent said they did not and 17 per cent said they did not know.
This compares to nine in 10 of those in their early forties who said they would still be teaching.
One male PGCE student in his early forties told researchers: "It's a long-term career change... it's longer than 10 years."
Professor Alan Smithers, an expert in teacher recruitment at Buckingham university, called on the Government to expand employment-based training.
"Learning on the job gives students a much better idea of what teaching is really like," he said.
Helping young people to learn (98 per cent) and working with children (92 per cent) were the factors most likely to attract people to the profession, particularly among women and primary teachers.
Financial incentives such as training salaries in shortage subjects were attractive to more than half of men but just 38 per cent of women.
Secondary teachers were more likely to be attracted by the opportunity to continue with a subject specialism and by opportunities for career development.
The report said: "The altruistic motives which appear to lie behind many student teachers' decision to enter training are particularly encouraging in terms of teacher retention."
Previous research suggested that teachers motivated by unselfish reasons are more likely to remain in the profession, it said.
Why people choose to become teachers and the factors influencing their choice of initial teacher training route: early findings from the Becoming a Teacher project was written by academics from Nottingham and Leeds universities and the MORI Social Research institute. It is available on the web at www.dfes.gov.ukresearch