The study commissioned by the School Teachers' Review Body found that the average number of hours worked per week had fallen from 51.3 in 2000 to 50.8 for secondary classroom teachers.
Primary teacher hours dropped from 52.8 to 51.8 in the same period while special school teachers registered the biggest fall - from 51.2 to 47.6 hours.
The survey, based on diaries filled in by 2,700 randomly selected teachers during March 2003, also showed a slight easing of workload in the past three years for heads of department and assistant and deputy heads in secondary schools.
Primary heads were the only ones enjoy a significant improvement with weekly hours falling from 58.9 to 55.5. Their assistants and deputies, along with secondary heads, saw a slight increase.
The overall picture looks worse when compared to the situation in 1994, the first year the review body conducted the survey.
Back then primary and secondary classroom teachers worked only 48.8 and 48.9 hours respectively with special school teachers clocking up 47.5.
Hours for primary deputy and assistant heads have risen significantly in the past nine years from 52.4 to 56.4 as have those for secondary heads of department from 50.7 to 52.7.
Workload for primary and secondary heads and secondary deputy and assistant heads remains broadly the same today as in 1994.
The survey also showed that on average women worked slightly longer hours than men and that Year 4 teachers appeared to have slightly longer hours than others.
Doug McAvoy, National of Teachers' general secretary, said the survey showed little improvement in teacher workload and warned that even this could disappear due to teacher redundancies and worsening pupil-teacher ratios.