Two-thirds of teachers believe exam league tables are damaging their careers, according to a survey.
The poll, by the Teacher Support Network, an independent charity, reveals that most teachers believe the pressure of meeting exam targets contributes to increased stress and workload.
The findings add fuel to condemnation of the tables by trade unions who say they are divisive and give a skewed picture of school performance, as staff "teach to the test" to inflate their schools' table positions.
The Teacher Support Network surveyed 310 primary, secondary and special school staff across England and found that 64 per cent felt the tables caused extra stress. Only 6 per cent said they had a positive impact on schools.
The findings have been released a week before the publication of the secondary league tables by the Department for Education and Skills.
One teacher at a special school in Essex, which caters for children aged five to 16, told The TES this week: "I have been asked to do nothing but Sats papers from March onwards for some classes just to make sure they perform well in the tests that summer. We do the same for the GCSEs.
"The pressure on teachers just seems to mount. We find that straight after the exams the sickness rate in this school trebles. It is all down to stress."
In 12 months, the Teacher Support Network dealt with 973 teachers complaining of stress and 738 worried about workloads.
According to its survey, only 21 per cent felt supported by their headteachers. More than half claimed that this lack of support had a negative effect on pupils' performance in the classroom.
The findings mirror a TES survey published last week in which seven out of 10 teachers said their workload had increased over the past four years.
Patrick Nash, chief executive of Teacher Support Network, said: "There is a great deal of debate about the usefulness of league tables, but what is obvious from our survey is that the majority of teachers see them as a source of stress.
"Many feel that pressure to meet targets is stifling teacher creativity and taking the enjoyment out of teaching and learning."