Seven out of 10 felt the practical approach of the graduate and registered teacher programmes would stand them in good stead.
But 58 per cent of the 300 trainee teachers surveyed by the National Union of Teachers had concerns about some aspects of their training, rising to 62 per cent in secondary schools.
Nearly two in five respondents cited lack of support from schools, universities and training bodies and a quarter were unhappy with the training, particularly subject knowledge and teaching theory.
More than a fifth struggled with workload, citing difficulties balancing teaching and studying. Those with heavy teaching loads and subsequently restricted training opportunities were most negative.
Trainee teachers in primary schools were more likely to be teaching for more than 20 hours a week compared to their secondary colleagues. Some complained of being used as "cheap labour" to plug unfilled vacancies and being left to "sink or swim".
"This is not training as I understand it," said one respondent. "I am a 'cheap pair of extra hands'. Teaching colleagues are great, but it is really up to me to sort out my own training."
The survey comes as the Teacher Training Agency looks to double the number of places on work-based routes over the next three years to a fifth of all places. Around 4,200 have been allocated for September.
The GTP pays up to pound;13,000 towards a graduate's salary, plus pound;4,000 for training. The registered teacher scheme allows non-graduates to train on the job over several years while completing a degree.
John Bangs, NUT head of education, said more improvements were needed to the programmes.
"By luck and goodwill, the majority of people on these programmes think this is the right route for them but there is not enough support in schools for trainees and the mentors. There is a worrying minority who feel they are being short-changed."
He said expansion had to be on the basis of proper financing and support and provision of training as in-depth as a PGCE.
The TTA said complaints about trainees being left to "sink or swim" were rare, and it was planning further support and to improve the quality of training.