More than two fifths of supply teachers say they are being used to cover the lessons of naughty pupils, a survey has found.
A poll 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 nearly 900 UK supply teachers, found that 42% say they feel they are used to cover the lessons of more difficult pupils.
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.
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: "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 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."