The focus on the attainment gap and the “wild misreading of Pisa data” have combined to create an image that Scottish education is “rampantly failing”.

But that image is simply not true, insists Colin Mair, outgoing chief executive of the national body that analyses huge amounts of local education data.

According to Mair - who has just retired as chief executive of the Improvement Service, having taken the job in 2004 - Scottish education has been on “a journey of continuous improvement” and the attainment of pupils from the most deprived areas has improved fastest.

He concedes in an exclusive interview with Tes Scotland that a “horrible” attainment gap exists between rich and poor. But Mair believes the system is currently producing “the best-qualified generation of Scots, without a doubt”. National qualifications - not the disappointing results in the Programme for International Student Assessment (Pisa) - should be used to measure the Scottish system’s success, he argues.

However, Lindsay Paterson, professor of education policy at the University of Edinburgh, challenges Mair’s downplaying of Scotland’s Pisa results, arguing that attainment data cannot be compared over time because exams today do not measure the same things as they did a decade ago.

Mair says: “There are deeply compelling statistics and data on the level of the improvement in the system: we have increased the number of kids moving from school to higher education; we have increased the average tariff score.

“This is the best-qualified generation of Scots in history, without a doubt, unless you are wanting to go the whole hog and embrace the conspiracy theory that says this improvement is entirely to do with dumbing down.”

He says the attainment gap is “still horrible, large and substantial”. But he stresses that children from poorer communities are doing better educationally than in the past, and that the teachers who are driving improvement “deserve to have that recognised”.

Mair also argues that the way attainment is measured - the point at which teenagers leave school - exaggerates the size of the gap. He says it should be measured at the age of 18, reasoning that if a pupil leaves school at the end of S4 for college and goes on to be awarded a Higher National Diploma, that achievement is not acknowledged, yet the achievements of those who stay on at school for another two years are counted.

“If we compared like for like at age 18, the gap would still be there, but it would not be on the same scale as it presently is,” he says.

Irrespective of the size of the gap, it is still of “absolutely fundamental importance” that Scotland closes it, he says, as the country contends with an ageing population, along with the likelihood of immigration restrictions post-Brexit.

Larry Flanagan, general secretary of the EIS teaching union, says: “The EIS has been saying for some time that the narrative of apparent failure around Scottish education, propagated by politicians desperate to score points off each other, and aided and abetted by sections of the media keen to create sensationalised stories, has been hugely damaging to the morale of the profession and deeply disrespectful of the very real achievements of our young people.

“While we do need to recognise that improvements are still required, the fact is that we have a high-performing education system here in Scotland.”

A Scottish government spokesman says that “Scottish education is good and is getting better”, adding that there is still work to do to ensure all children “have the best opportunity to succeed regardless of their social circumstances or additional needs”.

He says that ongoing educational reforms “will see more money and power going to schools to raise standards for all and close the poverty-related attainment gap”.

The spokesman adds: “We currently have the lowest ratio of pupils to teachers since 2010, better-quality school buildings, and the vast majority of children in S3 achieving the minimum attainment level expected of them, or better.”

The government says that the most recent exam results show many students are leaving school “with a greater range of qualifications, skills-based awards and achievements under Curriculum for Excellence”.

@Emma_Seith