Sixty per cent of second-level school classrooms are overcrowded, with more than the recommended maximum of 30 students in each class, according to a new survey.
Carried out in 214 schools by the secondary teachers' union, ASTI, the survey also found that 30 per cent of schools had difficulty, because of inadequate staffing, in providing the full range of science subjects.
Among the subjects which have suffered most from staff shortages have been technical graphics, computer science, applied mathematics and chemistry.
This is at a time when politicians and industrialists are repeatedly stressing the importance of students taking computer and science subjects for the good of the national economy.
Forty-two per cent of schools surveyed said they have had difficulty in providing the full range of technical subjects because of inadequate staffing.
ASTI general secretary Mr Charlie Lennon said yesterday he was surprised that the survey showed there had been "little or no improvement in the staffing situation" since the union's last survey three years ago, "in spite of ministerial initiatives on staffing which clearly have made little or no difference".
This was happening "at a time when the State is benefiting from record revenue returns which would enable it to make the necessary investment in our schools".
He warned that the findings would "bolster calls at our forthcoming annual convention for immediate balloting on industrial action in order to force the Government to tackle this schools crisis as a matter of urgency".
The survey showed that in 59 per cent of second-level schools, academic subjects were taught in classes of more than the Government-recommended maximum of 30 students. A quarter of them had between four and 12 classes with more than this maximum.
In the same proportion of schools, practical subjects are taught in classes of more than 24 students, with 21 per cent of schools having more than seven classes in this situation. Forty-five per cent of schools said they had been prevented from adding new subjects because of lack of staff.
The subjects most affected were music, which 12 per cent of schools said they could not offer; technical graphics (12 per cent); computer science and applied mathematics (10 per cent); German, engineering, construction studies and technology (all at 8 per cent).
Twenty-six per cent of schools said they had been forced to drop subjects due to lack of staff. The subjects most affected were chemistry (6 per cent of schools), economics (5 per cent), German and music (both 4 per cent).
Seventy-five per cent of schools said that because of teacher shortages they had to provide Leaving Certificate higher level and ordinary level in the same classroom. Similarly, 69 per cent of schools had to provide Leaving Certificate ordinary level and foundation level in the same classroom.