SCOTTISH teachers work an average of nine extra unpaid hours a week, according to a new survey.
The Educational Institute of Scotland (EIS) teaching union, which commissioned the research, said the additional hours worked were more than in any other graduate profession.
The findings are consistent with research undertaken by Glasgow University in 2006 which indicated that teachers were working around 45 hours per week, with promoted staff working around 55 hours.
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The survey findings were published a week after it was revealed that the number of cases of teacher stress which result in compensation has doubled in a year.
Scottish teachers already have one of the highest teaching workloads in the developed world.
Larry Flanagan, general secretary of the EIS, said a long- hours culture was not conducive to the health of Scotland's teachers.
"Teaching is a highly stressful job. We have seen an increase in punitive and less supportive absence management procedures over recent years," he said.
"However, little attention is paid to the long-term impact when teachers feel pressurised to turn up even when ill or feel pressurised to work long hours.
"There is no doubt that the current culture stores up long- term problems and has led to a growth in psychological issues relating to employment."
He added: "We are well aware that stress is rising in the public sector, with job losses and pay freezes destabilising highly motivated employees such as teachers."
However, Douglas Chapman, education spokesman for Cosla, the council umbrella body, said teachers were not alone in doing a "challenging job".
"The vast majority of teachers work extremely hard, and their effort and dedication is recognised and respected by staff, parents and pupils," he said.
"Teaching is not an easy job, and it brings with it a range of challenges, but it is also fair to say that the challenge of educating children is often what attracts people to the profession in the first place.
"Local authorities take their responsibilities to staff extremely seriously and do what they can to manage stress in the workplace, and in difficult financial circumstances local government is also doing what it can in the current round of pay negotiations to respect the hard work teachers put in throughout the year, and to maintain employment levels. Teachers may do a challenging job, but they don't do it alone."
A Scottish Government spokesman said: "We will continue to work with teachers' organisations and local authorities, through the Scottish Negotiating Committee for Teachers, to monitor teacher workload and other aspects of teachers' conditions of service.
"During recent discussions with the EIS, the Education Secretary was clear that he is willing to hear and discuss the findings of the survey."
The Organisation for Economic Co-operation and Development found school staff in Scotland spend an average of 855 hours a year teaching – compared to an international average of 704 hours.
Only teachers in Mexico, the United States, Chile and Argentina spend longer in the classroom.