THE salaries of Scottish teachers are slipping further behind their international colleagues, according to new figures.

A major report on education systems around the globe found the value of pay for secondary staff in Scotland is ranked 21st out of 34 countries in the developed world, compared to 17th the ­previous year.

The Organisation for Economic Co-operation and Development (OECD) found the value of salaries paid to unpromoted Scottish teachers - who can earn over £34,000 a year - has been overtaken by school staff in Finland, Italy, Norway and New Zealand. The best paid teachers are in Luxembourg, Switzerland, Germany, Korea and Belgium.

The Education At A Glance 2014 report, which blamed the economic downturn for the fall, reinforced warnings from unions that teaching in Scotland no longer commands a competitive salary compared to other graduate jobs.

The OECD report also found pupil-teacher ratios in Scottish primary schools have risen sharply, despite Government policies to reduce class sizes.

In its 2007 manifesto, the SNP promised to deliver class sizes of 18 or fewer in each of the first three years of primary school, but the number of pupils per teacher has grown from 14.6 in 2011 to 21.1 in 2012.

Teachers in Scotland also work some of the longest hours in the developed world. The report finds secondary school staff spend 855 hours in the classroom a year compared to an international average of 700 hours. Only teachers in Argentina, Chile, the US and Mexico spend more time teaching.

Larry Flanagan, general secretary of the Educational Institute of Scotland teaching union, said: "The reality is that there has been gradual erosion of real-terms pay and living standards over the past decade. The problem has been particularly acute over the last few years following the economic crisis and the Government's enforced pay freeze that followed.

"The pay freeze, coupled with subsequent below inflation pay awards both last year and this year, has increased the financial strain on teachers at a time of soaring workload and the huge pressure of delivering a major programme of curricular change."

Mr Flanagan also highlighted spiralling pupil-teacher ratios, adding: "Rising workload for teachers, together with larger class sizes for pupils, is an extremely worrying combination that must be addressed to ensure both a reasonable work-life balance for teachers and a high-quality learning experience for young people in our schools."

Alan McKenzie, acting general secretary of the Scottish Secondary Teachers' Association, said: "It is not surprising and we have tried to make this clear to councils and the Scottish Government, but it has fallen on deaf ears so far with austerity the only answer.

"They need to come to terms with the fact there is sharp erosion in salaries and you will not attract the best graduates to the profession in spite of the popular myth that people are glad to become teachers. The pupil-teacher ratio is ­variable, but Government measures have not reduced this as intended and that makes teaching more challenging."

Andreas Schleicher, the OECD's director for education and skills, said nations across the developed world were having to make a "trade-off" between smaller class sizes or paying teachers more - with many high-performing countries choose the latter.

He said: "You can spend your money only once, so if you have a fixed amount of money that's the kind of trade-off you have to make. Smaller classes limit your capacity to pay teachers better, and that's the trade-off you can see in the data. Finland, Japan, Singapore, Korea - those countries prioritise teaching and teachers over infrastructure and class size."

Across the UK, the report found three-quarters of university students graduated without the highest levels of literacy or numeracy, despite studying at degree level. In high-performing countries such as Australia, Finland, Japan, the Netherlands and Sweden, more than one-third of graduates perform at this level for basic skills.