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Scotland's disappointing results in the Pisa international assessments beg a very obvious question: is Scotland's education system worse than it used to be?

Like many simple questions, the answer is not so straightforward.

There is no denying that there is nothing to celebrate in the Programme for International Student Assessment (Pisa) figures and much to cause real concern.

For the first time since the tests began in 2000, Scotland was merely ranked as "average" in all three categories measured - reading, maths and science.

Once Scotland was classed as "above average" in all three.

For an advanced country which considers education to be a source of pride to be ranked like this should be a cause for concern.

The fact things would seem to be going the wrong way after a radical change - the introduction of Curriculum for Excellence and the shake up to qualifications - should make that concern greater.

While the Pisa statistics do not paint a pretty picture of Scotland's performance over the past decade and a half, what about the longer term picture?

The idea that Scotland's education system was once the envy of the world owes much to folklore.

There is no simple, objective way of saying how the quality of Scottish education in, say, the 1950s or 1980s compared to education in other parts of the UK or other advanced western countries.

Important as the Pisa figures are, they are not a definitive measure either and some consider them flawed. Most importantly they do not measure what the young people go on to do with their education.

It is interesting to reflect on how the day-to-day experiences of teenagers in schools today may compare with that of their parents.

Until the 1980s, the start of third year was a watershed moment for students.

The academically able usually began studying for eight O Grades. The presumption was they would then go on to study for four or five Highers in fifth year.

The most able would then spend sixth year studying for more Highers, improving the grades in subjects they did not do so well in or studying for a Certificate of Sixth Year Studies to help ease their path to university.

But for the less able the path was different.

A youngster who was not able to study for eight O Grades would fill their timetable with "non certificate" courses.

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After the school leaving age was raised from 15 to 16 in the mid 70s, less able youngsters were faced with spending two years at school with little to show at the end. In some cases, this may have added to the risk of indiscipline as well as sheer boredom.

This concern led to the creation of Standard Grades - every youngster would get a Standard Grade for completing a course so S3 and S4 would no longer be a waste of time for the less academic. What mattered was the level of the achievement.

That ethos has been carried over into the new qualifications system. S4, S5 and S6 now form the "senior phase". The overwhelming majority of teenagers stay on until S6. S5 and S6 are no longer the preserve of the academically able. The emphasis is on what qualifications a youngster leaves school with - not what they have got at a particular stage.

At its best, this should mean all youngsters leave school with something of value. It would be unusual to leave with little or nothing - something which was widespread until the 1980s.

If a teenager is not in education, work or training now there is usually a back-story to explain this. At the other end of the spectrum, exam passes are at a record level and so is the number of young people at university.

In a more general sense, the ethos in many secondary schools has also changed. There is now much more of a concern for the development of the student as a person - how to nurture a successful, confident individual. Personal development was, on occasion, overlooked in secondary schools in the past with the focus more narrowly on academic performance.

The overall condition of school buildings is better than it was in the 1970s or 80s too.

While there are important issues concerning the quality of the construction of some new school buildings - for example in Edinburgh - at a superficial level the school estate across Scotland is in a better condition. Schools are more likely to be attractive, welcoming environments.

And industrial relations are better too. For all the very real concerns of teachers' unions - for example over workload associated with the new qualifications - the relationship between unions, the Scottish government and councils is generally respectful, friendly and constructive.

Compare that to the disruption caused by long-running teachers' disputes in the mid 70s and mid 80s.

And yet, and yet.

One question may be whether the most academically able are always being sufficiently stretched.

Another may be whether the good intent behind Curriculum for Excellence meant teachers were pulled in too many different directions and overlooked basics like numeracy and literacy - recently issued guidance re-emphasises their importance so no teacher can be left in doubt.

Questions over budgets and drops over the years in teacher numbers come to the fore as well. (While the number of teachers has fallen in recent years, councils now have to maintain the ratio of staff to students so cannot simply close posts or choose not to fill them.)

Meanwhile some parents remain to be convinced that the changes to qualifications have been for the better. If nothing else, if a youngster can only study for six qualifications in S4 (increasingly becoming the normal practice) it inevitably leads to a drop in the numbers studying some individual subjects.

The Pisa figures are not the last word but should provoke fresh debate on the Scottish school system. Why are these figures going the wrong way? Is the problem money? Poverty? Implementation? Guidance to teachers? About how schools are governed? Or more fundamental?

But they do not tell us anything about outcomes or the experience of young people.

So is the school system worse than it was? As a teenager might say on Facebook: "It's complicated..."