Scotland's performance in maths and science among 15-year-old school pupils is at a record low according to new statistics.
Reading levels - students' ability to understand and evaluate texts - have improved, but are still significantly lower than they were at the start of the millennium.
The new PISA figures for the 36 countries of the Organisation for Economic Co-operation and Development, show that ten are performing better than Scottish pupils in reading.
Maths and science
However maths and science have continued to decline, and Scotland now sits 25th and 24th respectively when compared to the other OECD countries. It is below both the English and UK average in both.
The figures also suggest that the closure of the attainment gap has stalled since the last round of PISA tests in 2015. The report states an 86 point gap between the reading scores of the poorest and wealthiest pupils - equivalent to three years' schooling - up slightly from 83 points the last time the tests were carried out. The attainment gap in maths gap has fallen from 87 to 83 points in the same period, with science up slightly from 97 to 98 points.
The random testing of Scottish pupils took place between last October and December and involved 107 secondary schools across state and private sectors, with a total of 2969 students taking part.
It is the seventh time Scotland has taken part in the three-yearly PISA analysis, which shows the mean scores for every country. Reading was at its highest level in 2000 when Scotland scored 526 compared to today's figure of 504 - although that is a rise from the 2015 result which saw it hit its lowest point of 493.
In maths, Scotland's high point was in 2003 with a score of 524, which has now fallen to 489; in science the high water mark was in 2006 at 515, with today's figure standing at 490.
Today Education Secretary John Swinney welcomed the improvement in reading, and said it was the result of the government's literacy attainment challenge which was introduced in 2015 when the PISA reading score had fallen to 493. He said that maths and science were also being "being tackled".
“These are very encouraging results and the latest sign that our education reforms are working," he said. "Scottish schools are improving and this international study confirms that.
“Reading underpins all learning, and the sharp rise in performance is good news."
He said the improvement had been "driven by great teachers and well-supported pupils" and the government's "unrelenting focus on improving literacy through the Scottish Attainment Challenge and Pupil Equity Fund. Those efforts are now paying dividends, with only five countries scoring higher than Scotland at reading."
Despite the figures for maths and science showing steady decline, Mr Swinney described the scores as "stable" and at the OECD average. However he added: "We need to see the kind of improvement that we now see in literacy in these areas too. That is the challenge.
“An inspection of maths and numeracy published by Education Scotland shows what is working and how we can improve. It will help as we move on the next phase of driving up standards in Scotland’s schools.
“And, in science, good progress has been made with delivery of our five-year STEM strategy, with the roll-out of career-long professional learning grants and new online resources for teachers. The impact of it will only just be beginning to be felt on the ground and we will continue to push for the improvements that we know can be made.
“There is plenty of work still to do to improve Scottish education but today’s report should give people a strong sense that we are on the right track, making substantial progress and seeing results where it counts – in the classroom.”
'Failing schools and children'
However, the PISA scores were described as proof the government was "failing schools and children". Scottish Labour’s education spokesperson Iain Gray said: “While Nicola Sturgeon tours the TV studios and election debates boasting of her supposed achievements, the reality is that her so-called priority of education continues a slow decline.
“The small improvement in reading is welcome, but further falls in maths and science are alarming. John Swinney and Nicola Sturgeon have been warned again and again that we have a problem with STEM subjects being squeezed out of the curriculum but they refuse to listen. These are the critical skills our next generation need for the jobs of the future."
He added: "John Swinney persists with unwanted and unhelpful “reforms” like his standardised tests while failing to ensure that our schools have enough resources and enough teachers with enough time and support to do the job we know they can.
“The SNP have abolished most measures of performance in our schools, but they cannot hide from these figures which show they have failed our schools and our children.”
And Liz Smith, Scottish Conservative education spokesperson, said: “This is damning evidence revealing the full extent of the SNP’s shameful 12 years running down Scotland’s schools.
“Nicola Sturgeon asked to be judged on education. This summer saw the fourth consecutive year of decline in Higher pass rates and now the SNP is presiding over the worst ever PISA results in both maths and science. In reading, where it should be acknowledged that there is encouraging improvement since 2015, the score is still lower than the 2012 result and considerably lower than the score in 2000.
"Performance in maths and science is absolutely vital for the future of Scotland's economy and for industries such as engineering and IT. These results are a humiliation for the SNP and they also mean that the potential of Scotland’s economy has been tarnished.
“After the last set of poor PISA results, the SNP said that the curriculum had to change. Yet these results are a new low and we know there have been many failings within the delivery of the Curriculum for Excellence. It is not just time to change the curriculum but also to change the government in Scotland.”
Scottish Liberal Democrat leader Willie Rennie added: "John Swinney can't hide from these appalling results.Scotland used to have one of the best education systems in the world, but under the SNP its now just average.
"Scottish teachers have been messed about for too long. John Swinney has refused to listen to them. Support in their classrooms has been cut to the bone and they simply don't believe in the policies being imposed on them, not least the national testing of four and five-year-olds.
"Nicola Sturgeon once claimed education was her top priority, but nobody is now in any doubt that the SNP will always put independence first no matter the cost."
Scottish Greens Education Spokesperson Ross Greer MSP said that international comparisons "should rarely be taken at face value" and that while PISA was "useful in context" it wasn't required "to tell us what the problems are in Scottish education."
He added: "Years of budget cuts, thousands of lost teaching and support staff and a near total failure to support children with additional needs are at the root of many of the problems our still relatively robust education system now faces.
"The major barrier now is an SNP government unwilling to address these problems and which is instead still pursuing governance reforms so unnecessary, unwelcome and unhelpful they couldn't even get them through Parliament."