Almost half (45 per cent) of heads believe they do not have enough teachers, and a third have said there are not enough support staff and materials, according to the respected Pisa worldwide education survey.
Education secretary John Swinney last week unveiled plans to hand £120 million of funding direct to schools as part of a drive to tackle the attainment gap between rich and poor areas of Scotland. The cash will allow heads to bring in extra teachers, or fund measures like extra tuition or IT equipment.
But Labour insisted that the Budget deal agreed by the SNP and the Scottish Greens last week will mean £170m is axed from local services and that schools will be among those to suffer.
Labour education spokesman Daniel Johnson said: “Schools in Scotland are struggling because of a decade of SNP cuts to education. The SNP’s budget deal with the Greens means that local education budgets will have been slashed by £1.5 billion since 2011.
“This is Scotland’s head teachers saying that there are just too few staff in our schools. Yet the SNP-Green budget forces even more cuts onto schools.
“Since the SNP came to power there are 4,000 fewer teachers and 1,000 fewer support staff in our schools. Headteachers are now telling the SNP that this is harming our country’s future, but the Nationalists still won’t listen.
“There is still time to choose a better path. The Budget has not been finalised yet. Labour’s plans to use the new powers of the Scottish Parliament to stop the cuts and invest instead would mean more funding for our schools, and a better future for Scotland.”
Labour is calling on the Scottish Government to use the new tax powers given to Holyrood to offer more support for schools. Labour has also proposed a 50p top rate of tax on the richest few to invest in education.
The Pupil Equity Fund unveiled by Mr Swinney will see thousands of headteachers across Scotland receiving funding of up to £300,000 in poorer areas to be spent on measures to improve attainment as they see fit. The allocations are based on the number of pupils from P1 to S3 known to be eligible for free school meals, with schools receiving around £1,200 per pupil.
Speaking as he launched the scheme last week, Mr Swinney said: “We are providing additional ring-fenced funding which will enable individual schools to target support where it is needed the most.”