Scotland's largest teaching union has called for a reduction in class sizes to enable staff to cope with increasing demands.

The present limit of up to 33 pupils per class was set in the 1970s.

However, the Educational Institute of Scotland (EIS) said the figure was no longer compatible with teaching methods and a limit of 20 pupils per class should be introduced.

Scotland is well down the international league table on class sizes, with Poland, Portugal, Belgium and Spain among the countries with smaller classes.

The Scottish Executive has already cut class sizes to 30 for the first three years of primary school.

We need to move into the 21st century Ronnie Smith, EIS

But EIS General Secretary Ronnie Smith said that is not enough.

"The current class size limits were established in 1976 and by the end of the next Scottish Parliament it will be 30 years since that figure was established and I do think that we need to move into the 2ist century," he said.

"It's about improving pupil attainment and giving individual pupils the attention of the teacher that they need.

"It's also about creating a level playing field with the independent sector, where average class sizes are smaller."

However, Education Minister Cathy Jamieson warned that cutting class sizes would be a long term process.

Ms Jamieson told BBC Scotland: "It's not the case that we would simply be able to do this overnight.

"There are a number of other things that we need to do, including the provision of suitable buildings and equipment, classroom assistants and other support staff.

"What we have said is that we will consider looking at how we may reduce class sizes, perhaps in the first and second years of secondary school as a priority."

'Important improvement'

The EIS also said international data showed some connections between class size and pupil performance.

It said that although additional classroom assistants can help ease the burden, they are no substitute to cutting the size of classes.

SNP education spokesman Mike Russell welcomed the call.

"The EIS campaign is recognition that this is the single most important improvement we can make in education and their timely campaign is most welcome," he said.

"The consensus for change is now almost universal among parents and teachers, but successive Westminster governments and Labour in Holyrood have failed to make inroads in the last quarter of a century."