It used to be said Scotland had the best education system in the world. Whether that was ever objectively true or not is another matter.
Scotland certainly once prided itself in having the best school education in the United Kingdom, and there historical evidence that was the case.
On mathematics and science, Scotland is behind England in the latest assessment of the tests carried out in countries across the world, and at a similar level to England in reading.
However, that only tells part of the story. What should be most troubling for politicians and policy-makers is the long-term decline in all three subject areas north of the Border.
Although it has gone up and down over the years, on reading Scotland has fallen from a score of 526 in 2000 to 504 in 2018.
In maths, the fall has been consistent in each every three years the tests are done, down from 524 in 2003, the first year it was tested, to 489 in 2018. And in science the historic trend has also been down, from 515 in 2006, again the first year it was tested, to 490 for 2018.
The figures also show that of the four nations that make up the UK, England had the highest scores in all three subject areas in this latest survey. The Scottish government today said the figures showed "reading levels among Scotland’s children have risen sharply in the last three years and the attainment gap is closing".
They added PISA shows the relationship between performance and social background is lower than the OECD average - lower meaning there is less of a relationship between your background and learning.
Closing the attainment gap between pupils from poorer and better off backgrounds has been one of First Minister Nicola Sturgeon's key priorities in government.
In a media release John Swinney, the Deputy First Minister and education secretary, said: “These are very encouraging results and the latest sign that our education reforms are working.
"Scottish schools are improving and this international study confirms that.
“The figures on social background also confirm that we are closing the gap between pupils from the richest and poorest backgrounds."
However, his view is disputed by . Prof Paterson says: “Scotland’s results are even worse than three years ago, when the outcome was widely seen as dismaying. Attainment in mathematics and science has continued to decline. The upturn in reading attainment has only brought the country back to where it was a decade ago."
Scotland’s results are even worse than three years ago, when the outcome was widely seen as dismaying.
"By contrast, attainment in England has risen significantly in mathematics and reading, and in science has declined much less than in Scotland."
"The socio-economic attainment gap has fallen in England as much as in Scotland. In England this has been achieved by boosting the attainment of students facing difficult social circumstances. In Scotland, lower inequality has come about partly by depressing the attainment of the well-off."
Prof Paterson says that the statistics - for reading ability - in the full PISA report prove his point about the attainment gap.
It's complicated, but if you compare the top quarter of pupils in England and Scotland with the bottom quarter, the lower group north and south of the Border improved.
But Prof Paterson says the scores for the higher status pupils in England went up, but for their equivalent in Scotland it went down, allowing the Scottish government to say the gap is closing.
However, the long-term trend on these figures has led Prof Paterson to a further conclusion relating to the Curriculum for Excellence (CfE) introduced in 2010, which aims to "put learners at the heart of education".
Scottish education urgently needs someone to take responsibility for leading our schools out of this crisis.
Prof Paterson says: "Scottish school policy is simply not working. Every political party is to blame, because all of them have supported the reforms to Scottish education that are now evidently disastrous.
"Yet Scottish education urgently needs someone to take responsibility for leading our schools out of this crisis.”
I put the point about the curriculum to Mr Swinney are a media briefing this morning, asking if it the PISA figures exposed a fundamental problem? His reply was a firm "No".
He also dismissed the suggestion that these figures show reforms in England, made by the then education secretary Michael Gove, a Scot, seen as a move back to more 'traditional' forms of learning, were more successful than CfE.
Mr Swinney and the Scottish government believe that CfE with its emphasis on giving young people "knowledge, skills and attributes to thrive in our interconnected and rapidly changing world" (to quote the official definition) is the way forward.
Given that it was supported by all the political parties, the teaching unions and most parents groups, there is little chance CfE will be scrapped, though there is talk of further reform.
PISA is not the only measure of Scottish education. There will be statistics out next week on the new standardised assessments of pupils at P1, 4, 7 and secondary 3, though they cannot be compared with other historic measures as the system is different.
Are there other international comparisons that can be made? Yes, but not for Scotland as the Scottish government pulled out of Trends in International Mathematics and Science Study () and Progress in International Reading Literary Study ().
So it may be another three years before we know whether Mr Swinney and the Scottish government are right in maintaining their faith in the new curriculum and their belief that it will improve Scotland's education in terms of comparisons with other countries, including our nearest neighbours.