I’m often asked by parents for my views on the current state of education in Scotland. I try to be even-handed and fair, but such analysis of our standards, and whether or not they are falling or improving, is almost impossible to ascertain.

Which begs the question, why do we have almost no idea if the education system is doing well compared with its historical past?

Well, I’m beginning to think that it is because the powers that be don’t want us to know.

Here are four issues that highlight this:

1. SQA results

The Scottish Qualifications Authority (SQA) marks all externally assessed examinations at National 5, Higher and Advanced Higher. To ensure the system is fair, it predetermines the percentage of pupils that will pass at particular grades. This is to take into account the vagaries of assessment materials.

That is why the pass mark for Higher maths has been as low as 34 per cent. One year, the Classics Higher had a pass rate of well above 50 per cent because, had the SQA not done this, every student would have “passed”.

Therefore, you cannot compare SQA results from one year to the next. The stats tell you almost nothing.

Quick read: FMQs row over review into falling Higher pass rates

Quick read: Swinney hits out at ‘culture of negativity’

International data: What does Pisa tell us about Scottish education?

Timss and Pirls: Scotland ‘tarnished’ by avoiding international surveys

2. Timss and Pirls

The Scottish government withdrew from two international studies in 2010, namely Timss (Trends in International Mathematics and Science Study) and Pirls (Progress in International Reading Literacy Study). It suggested these comparative studies were too expensive to undertake (costing about £800,000 every four years).

However, on closer inspection, Scotland never made the top 10 in any test in any curricular area, while England and Wales regularly did.

Perhaps the real reason for withdrawal was because it was proving to be embarrassing.

3. End of SSLN

Then, in 2016, the government revealed that it would withdraw from its own annual study of academic standards, the Scottish Survey of Literacy and Numeracy. The reason given was that it was no longer required, as the government was introducing new standardised tests (to much criticism from educators).

The real reason may have been because these tests were showing clear signs that standards were slipping.

4. Pisa ratings

In December, the results from the Programme for International Student Assessment (Pisa) were announced.

Pisa is now the only benchmark we have that shows how we compare with other countries now and with our own country’s past.

Scotland’s mean score in reading was higher than in 2015, similar to 2003, 2006, 2009 and 2012, but significantly lower than 2000. The mean score in maths in 2018 was similar to 2015, but lower than in 2006 and significantly lower than in 2003. Scotland’s mean score in science in 2018, meanwhile, was similar to 2015, but considerably lower than in 2012, 2009 and 2006.

So what does all this mean?

The truth (according to Pisa) is that our national performance in reading, maths and science (while admittedly being above the OECD average) is considerably weaker than it was in 2000. In other words, what we are actually witnessing is a slow and steady reduction in attainment compared with our own nation’s historical evidence.

Instead of pretending everything is fine, the government would be well advised to get its finger out and get it sorted - or at the very least, acknowledge that there is indeed a problem.

Rod Grant is headteacher at Clifton Hall School, an independent school in Edinburgh. This article also appears on the school’s website