More than two fifths of supply teachers say they are being used to cover the lessons of naughty pupils, a survey has revealed.
A poll released on Friday by the NASUWT union suggests that it is inexperienced supply teachers who are most likely to say that they are asked to take these classes.
It also reveals concerns among supply staff about the lack of work available to them, with many being forced to claim the dole.
The survey, which questioned 849 UK supply teachers, found that 42% say they feel they are used to cover the lessons of more difficult pupils.
This rose to almost half among those who had been teaching up to two years, and those who had been in the classroom for between three and five years (48% and 49% respectively).
More than one in five (22%) of those surveyed said that they felt a request they have made for support with behaviour management had not been taken seriously.
The poll also found that nearly two fifths (38%) of supply teachers are resorting to this type of work because they are unable to find a permanent job - this rose to 41% among the women questioned.
And a third said that they wished to work five days a week (34%) but less than one in 10 (9%) said they were able to do so.
In total, nearly three quarters (73%) said they had found some problems finding supply work while 27% said they had found no difficulty.
A quarter (26%) told the survey that they have been forced to claim job seekers allowance (JSA) while 12% have claimed other benefits.
Around a third (32%) of 20 to 30-year-old supply teachers said that they had made a JSA claim, along with the same proportion of 41-50-year-olds.
NASUWT general secretary Chris Keates said: "It is increasingly clear that many younger teachers are taking on supply roles out of economic necessity.
"This is no way to begin a career in teaching as the structure and support will simply not be provided.
"The fact that nearly a third of young teachers are claiming Job Seekers' Allowance is a waste of a valuable resource and the investment made in their training.
"The survey also shows that some schools appear to be using supply teachers to cover the lessons of more difficult pupils.
"Over half of teachers with less than five years experience felt they were being placed in this position.
"The NASUWT is clear that when deployed appropriately, supply teachers are essential to ensure that teaching and learning for pupils is able to progress during staff absence."