Teachers have urged politicians not to use them as a convenient scapegoat for the problems in Scotland's education system.

First Minister Nicola Sturgeon has acknowledged that Scottish education is not good enough, with a decline in reading and writing skills and too many deprived children held back unfairly and denied the opportunity to go to university.

She said she is prepared to make tough decisions to improve Scotland's "unacceptable" education system, but the Educational Institute of Scotland (EIS) said this should not lead to more pressure being heaped on teachers.

The EIS also stressed that the recent drop in reading and writing skills recorded in the Scottish Survey of Literacy and Numeracy (SSLN) was only a "slight dip", mainly amongst the most impoverished children which "underlines the impact of austerity measures on young people".

MSPs will debate "equity and excellence in education" at Holyrood today, with Labour noting that teachers are under "severe strain" and the Conservatives calling for headteachers to be given more autonomy to be "more responsive to parent choice".

Speaking ahead of the debate, the EIS said schools and teachers are committed to tackling the impact of poverty but require the resources to do so, and said the education system "must not become a convenient political scapegoat for the very difficult societal challenges that poverty in the age of austerity can create".

EIS General Secretary Larry Flanagan said: "It is simply wrong and wholly unacceptable for any politician from any political party to attempt to blame schools or teachers for the problems of poverty in society.

"Schools themselves are facing serious challenges owing to falling budgets, scarce resources and cuts in staff numbers.

"The demands placed on teachers are growing, and workload and levels of stress and related illnesses are extremely high.

"Despite all of this, schools are working extremely hard to support pupils from all backgrounds and should be receiving not blame but both praise and more support for this essential role."

He added: "The findings of the SSLN also explicitly rule out any notion of declining standards as a full analysis indicates the maintenance of high standards with 80% of pupils measured as doing well or very well.

"Where a slight dip was identified - from before two years ago - this was focused mainly on pupils from the most impoverished backgrounds which is clearly a matter of serious concern but underlines the impact of austerity measures on young people."

Education Secretary Angela Constance will today insist that there "is much to be proud of in Scotland's schools, with children achieving record exam results, fewer young people leaving school with no or few qualifications and record numbers securing positive destinations on leaving school".

Scotland currently sits mid-table in the international rankings for school education, but Ms Constance will say "much more needs to be done to make all of Scottish education truly excellent".

"Tackling inequity by delivering excellence is a key priority for the Scottish Government," she will say.

"While the Scottish Government is committed to doing all that it can to eradicate poverty and that poverty can be a barrier to attainment, it should not be used as an excuse for failure.

"The Scottish Government has said that all options will be considered and that the evidence of what works will determine future policy, and calls on all involved, including parents, teachers, school leaders, employers and politicians, to play their part in overcoming barriers to delivering an education system that ensures that every child in every community has every chance to succeed at school and in life."

Scottish Liberal Democrat education spokesman Liam McArthur said: "The situation in Scottish schools is happening on the SNP's watch because they took their eye off the ball to focus all their attention on the referendum.

"The danger is that the SNP are now moving too slow to put this right.

"Liberal Democrats have said the top priority should be to give extra help to children from disadvantaged backgrounds to help them get on and achieve their potential. That approach has worked well in England and ends up helping all children in the classroom."