Every three years the Programme for International Student Assessment (Pisa), run by the Organisation for Economic Cooperation and Development (OECD), tests 15-year-old students from all over the world in reading, mathematics and science.

More than half a million 15-year-olds from 79 countries and economies took the Pisa test in 2018 - the focus was on reading.

The results of this Pisa will be released on Tuesday, 3 December. Here we recap on how Scotland fared last time around and the aftermath.

Remind us, what were Scotland’s Pisa results like in 2015?

Are you sure? OK. Scotland’s scores for maths, reading and science all declined in the 2015 Pisa figures.

Scotland ranked third of the four home nations in each category, with only Wales doing worse. In 2012, when the previous Pisa tests took place, Scotland was top in reading and maths.

Internationally, the tests in 2015 - sat by 15-year-olds in 72 countries and regions - showed that Scotland was considered “average” in reading, science and maths. In 2012, it was “above average” for reading and science.

Background: ‘Five years left’ to save CfE after Pisa plunge

Short read: ‘Pisa tests fail to recognise what’s important in education and should be ignored’

Long read: Rampantly failing? Not according to the data…

What were the actual scores?

In reading 493, down from 526 in 2000.

In maths 491, down from 524 in 2003.

In science 497, down from 515 in 2016.

The comparator years are different due to changes to assessment and scoring.

What was the reaction?

The results were released in December 2016, by which time John Swinney had been education secretary for seven months. Mr Swinney admitted the figures made for “uncomfortable” reading, but said he “wasn’t that surprised” by them, because the Pisa tests took place around the same time as the disappointing results of the 2015 Scottish Survey of Literacy and Numeracy.

Now, of course, there is no SSLN flare to warn of what might be in store for Scotland next week in the Pisa results - the government scrapped that survey and the last set of results was published in 2017.

What else did John Swinney say?

Well, in some ways the poor Pisa results were handy for him because they gave him a reason for the “radical reform of Scotland’s education system” that he was arguing at that time was necessary. He said: “It is by carrying through on these reforms - no matter how controversial - that we can make Scottish education world-class again.” But now he’s been in charge of education for three years and has had the chance to make his radical reform, bad Pisa results will be only one thing - bad news.

So, three years, on what has changed?

When the last set of Pisa results were published the school governance review was in full flow in Scotland. However, we now know, of course, that Mr Swinney eventually stepped back from legislating to hand more power to schools, opting instead to give councils a year to give their schools more control over spending and the curriculum. A year on he decided they had made enough progress for him to abandon his education bill once and for all.

The other change that was on the cards was regional education boards and now we have ”regional improvement collaboratives”. Finally, the controversial Scottish National Standardised Assessments were introduced in 2017.

So there have been changes, but do they count as “radical reform”? Probably not but then teachers won’t necessarily see that as a bad thing.

Anything else?

Well, one pretty major reason why Scotland might expect to perform better is that since 2015 the Scottish government has invested an additional £500 million in education, through the Attainment Scotland Fund. (Although there is, of course, some debate about how much difference this money can make when central education budgets are being cut to the core.) At the very least, though, the Scottish government must surely be hoping to see an improvement in terms of the link between social disadvantage and students’ scores.

What did others have to say about the results?

Professor Lindsay Paterson, of the University of Edinburgh, said the Pisa results showed that Curriculum for Excellence was “failing” and that they marked the worst news for Scottish education in his 30-year career.

Keith Topping, professor emeritus of education at the University of Dundee, said there was a need for urgent action to ensure that CfE was a success. He said Scotland had five years to get CfE right.

The EIS union general secretary, Larry Flanagan, stressed that the tests had been taken almost 18 months prior to publication, at which time “the upper secondary sector was undergoing major upheaval.”

The late Colin Mair, who retired last year as chief executive of the Improvement Service, which scrutinises and works with councils in Scotland, said: “We have remained in the top 30 per cent of countries. Whatever else that is, it’s not a catastrophe.”

Meanwhile, Maureen McKenna, Glasgow’s executive director of education and then president of education directors’ body ADES, said Pisa did not have the same resonance with the public in Scotland as it did in other countries, so teachers did not place the same emphasis on training pupils for the tests.