Classroom teachers south of the border are working up to two hours longer than they were two years ago but many spend less time teaching, according to the School Teachers' Review Body.
Primary teachers are working two hours longer and secondary teachers 1. 4 hours longer.
The figures are certain to put pressure on the Government to acknowledge the case for paying teachers more in recognition for the extra work forced on them by school reforms and years of growth in class sizes.
They come at a time when ministers are seeking a public sector pay freeze and amid signs of a shortage of teachers in some subjects. While heads and deputies in both sectors are working similar hours compared with the 1994 survey, heads of department in secondary schools are working 2.3 hours longer.
Between a third and quarter of teachers say they do not have the time to do their job properly. Many say they do more than a quarter of their work at weekends and during the evening.