I am not prone to anger. Indeed, as I age, I become more placid. In an age of fire and fury, of black and white, of weekend marchers and keyboard warriors, I find myself more likely to simply roll my eyes than to vent.

On Tuesday, though, I read the Scottish Government’s response to the release of the OECD’s latest Programme for International Student Assessment (PISA) data and anger seemed the only appropriate reaction.

“Scottish education maintains international standing” was quite the choice of headline to describe findings which show that Scottish schoolchildren are anything from eight (reading) to 18 (science) months behind where they were 15 years ago.

PISA is an imperfect measure - it covers only 15 year olds and only three subjects - but the fact that the continued decline surprised precisely nobody tells its own story.

This is not isolated; Scottish school education is on a journey from being excellent, to being good, to being average. That direction of travel is terrifying for parents but not, ostensibly, for the government’s education officials, whose press release suggests that our verified mediocrity is a cause for celebration.

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Scottish schooling in the devolution era is a tragic story, and the saddest thing of all is that this is a design rather than an accident. Michael Gerson, a speechwriter for former US President George W Bush, famously coined the term “the soft bigotry of low expectations”, and in Scotland we have effectively enforced low expectations. We have, quietly and gradually, institutionalised ambitionlessness.

Every parent or teacher, in every local authority, in every school, will have their own experience of the silent surrender of standards, and I have plenty. But all of this micro-level enforced averageness has been green-lighted by the smoke signals sent by the Scottish Government, tacitly supported, it must be said, by all parties of opposition in the Scottish Parliament.

It is time, now, to start again. The upheaval of yet another revolution in Scottish schooling will be tangible, but there is no other responsible choice. Moreover, no shibboleth should be off the table. Much of what has been attempted over the last quarter-century had good intentions, but as we know the road to hell is paved with them.

The concept of closing the attainment gap, for instance, sounds wonderfully cuddly and works perfectly as a political slogan. However, it is impractical and, frankly, undesirable.

I see the application of ‘closing the gap’ every day in my children’s school - in order to match the national political requirement, schools are closing the gap not by lifting those at the bottom but by suppressing those at the top.

If anyone wishes to write to The Herald’s letters page and tell me why this is a desirable outcome, I am all ears. And, in that letter, I’d be most grateful if you could explain the social and economic benefits of homogenising outcomes to the point where everyone emerges from school with the same qualifications, seeking the same university courses and the same jobs. Those four words - closing the attainment gap - always had more breadth than depth.

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‘Closing the gap’ should be replaced with ‘raising the level’. In practice, that means challenging children to excel. It means pushing those at the bottom to reach higher, and pushing those at the top to reach higher. It means allowing the rising tide to lift all the boats without worrying that the boats are all different sizes.

This is far from the only shibboleth to be challenged, but it is a decent place to start. Attention will focus, inevitably, on the Curriculum for Excellence. CfE is another sad example of input trumping output, and style trumping substance. The name, the intention, the foundation of CfE are laudable and even ambitious, but it has clearly been implemented in such a way as to make it entirely inconsistent with its own objectives.

This sits on the shoulders, now, of the Education Secretary, Jenny Gilruth. There are many people who could be blamed for the state of Scottish schooling, but Ms Gilruth is not one of them, having been in the job for only eight months.

Ms Gilruth has developed a reputation as a shrewd and tough operator, particularly in her last job in the macho world of transport. She is not a robotic politician; she is thoughtful and absorbs the views and evidence around her. She has already proven some tenacity, by committing to rejoin the other international comparators TIMSS (maths and science) and PIRLS (reading), which Scotland opted out of under a previous regime.

Furthermore, not so very long ago, she was a teacher.

My bet is that Ms Gilruth fully understands the scale of the problem in our schools. And furthermore, I’d lay money on her wanting, deeply, to fix it. The question, though, is whether she has the power to do what many of her predecessors have failed to do, which is to rock the boat against the wishes of the vested interests.

The trade unions, extremely powerful resistors to any education reforms, are the most obvious of those. However, increasingly, the Scottish Government’s own officials are proving to be blockers rather than builders.

This is true across the policy areas, with the civil service’s grip of Ministers and Cabinet Secretaries being tightened, and with the interactions between political leaders and their industries being increasingly sanitised and controlled.

Ms Gilruth’s success will depend on her willingness to take back control, and her stamina in holding firm when the vested interests place barriers in her way. Parents and teachers would support her in that; we elect the politicians, not their civil service handlers and not the trade unions, and we expect that the power to make changes lies with the people we elect.

Jenny Gilruth has the most important job in the Scottish Cabinet. We can talk about economic growth and tax, about our renewable energy future, about migration and demographic change; all important, but none as significant a shaper of our economic and social future as a country than education.

We are in the mud. Get us out.

Andy Maciver is Founding Director of Message Matters and Zero Matters