The Trades Union Congress warned this week that temporary workers risked being forced out of the workplace because they could not update their skills.
Brendan Barber, TUC general secretary, said employers and agencies were refusing to take responsibility for training temporary workers.
"Far from providing a bridge to permanent work, temps are in danger of being less likely to move into better paid, more secure work as their training at work is almost non-existent," he said.
Two of the biggest supply agencies, Synarbor and Select Education, agreed it could be challenging for temporary teachers to update their skills.
Unlike some small agencies, the two large agencies send their supply teachers on professional development courses, and in some cases provide them with mentors.
Both agencies objected to Mr Barber's characterisation of temporary work as a poor alternative to permanent jobs, saying that many supply teachers choose the flexibility of part-time work to give them time for family or other careers.
Select called for the Government to fund refresher courses for teachers returning to the profession.
"We need to get away from viewing temporary workers as second-class," said Peter Flannery, managing director of Select Education. "Some are running their own businesses in their own time. Some of our English teachers are budding novelists."
Helen Barnes, a 35-year-old who is expected to qualify for the Irish Olympics team in canoe slalom, is a part-time supply teacher in Nottingham, by choice. She works one week in three at primary schools, a schedule that allows her time to train.
"The children think I'm completely crazy to get up for training at 5.30 every morning before school," she said.
She agreed that supply teachers often fall behind in professional development and echoed Select's calls for government-funded refresher courses.
"I go to schools now with interactive whiteboards, and teachers leave work for me in the board," she said. "I just go, 'Oh my God - I'm going to have to learn how to use them properly.'"