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"We will recruit at least 3,500 additional teachers and classroom assistants and reduce teachers' daily contact time by an hour and a half per week to give them the time they need to lift standards."

That, in black in white, was the promise made by the SNP in the run up to the 2021 Holyrood election.

The commitment couldn't have been clearer: a specific minimum increase in teacher numbers, and an explicit reduction in class contact time, all for the express purpose of giving teachers the necessary time and space to improve the quality of Scottish education.

Why did the party make such a promise? To be frank, after years of getting things wrong when it comes to education policy, this was one of those rare occasions when they actually got things right.

Teachers' 'contact time' refers to the number of hours they spend actually teaching classes during each working week. This is in contrast to what is sometimes called 'prep time', during which educators must review students' work, plan forthcoming classes, prepare differentiated materials for pupils with additional support needs, complete paperwork, attend meetings, arrange their own professional development, and more.

Cutting contact time might seem counter-intuitive, because surely we want teachers to spend as much time teaching as possible? In reality, things aren't that simple.

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Look at it this way: if you are a parent, you'd probably like to think that your child's work and general progress are getting at least 10 minutes of attention per week.

That's not an unreasonable expectation, but when you do the maths you start to realise what it really means.

If an average primary school teacher with a class of 30 wanted to spend 10 minutes reviewing the work of each pupil (without even thinking about the other tasks they must complete) then they would need to be able to set aside six hours per week – or a full school day – purely for that purpose.

In high schools, where a teacher might have 150 students in total, 10 minutes per pupil per week would account for a total of 25 hours.

Right now, only a tiny fraction of those sorts of timeframes are available.

The high-quality teaching to which our children should be entitled can only happen when those in charge of the classroom are able to do all of their job properly and plan those learning experiences effectively.

The trouble is that in Scotland teachers have very little preparation time when compared to other countries, especially those considered to have the top-performing education systems.

Here, contracts mandate that all teachers deliver 855 hours of classroom teaching each year.

In Estonia, the figure varies from 585 hours for primary teachers up to 654 hours for those working in upper-secondary.

In Finland, the balance between primary and secondary is reversed, but teaching hours are still far lower than Scotland: their primary school educators deliver 673 hours of learning per year, while the figure in secondary schools is lower than 600 hours.

On the other side of the world, Korean teachers provide 617 hours of teaching at primary level, and as little as 517 hours in secondary schools.

Scotland is a clear outlier in these metrics: only four OECD countries have higher class contact time levels, and none of them are in Europe.

This whole issue is often discussed under the broad topic of 'workload', but it is not the case that teachers are demanding changes that would see them do less work: if anything, they're demanding the time and space to be able to do more work, more effectively.

And they are, of course, expecting the SNP to deliver on an explicit commitment that it made five years ago as it tried to win an election.

In order to keep the promise to cut contact time, the government needed to increase teacher numbers to at least 55,400 by the current academic year. In reality they fell nearly 2,000 short, meaning that today there are still fewer teachers in Scotland's schools than was the case when the SNP first took office in 2007.

That failure, and the consequent inability to keep the contact time promise, is the reason that schools could now be closed by nationwide strike action. If that does happen, responsibility for it will lie squarely with John Swinney, Jenny Gilruth, and the rest of the SNP.

In Scotland, contracts mandate that all teachers deliver 855 hours of classroom teaching each year. (Image: PA)

The government looks seriously rattled by this development, and this morning took the unusual step of sending out an updated press comment. It said that Jenny Gilruth is convening an emergency session of the national negotiating body in order to "back around the negotiating table." She is, apparently, "determined to find a resolution", although one might wonder why it has taken the threat of strike action during an election campaign to get us to that point.

They're even floating the possibility of giving councils even more money to increase teacher numbers, despite having spent more than £600m on that very thing in the last few years while failing to achieve their goals.

But the real problem is that any solution to this crisis won't be immediate, because increasing teacher numbers to the required levels cannot now be achieved before the coming Holyrood election.

That means that any resolution would have to depend on an assurance that these changes really are going to be delivered this time.

In order to escape the consequences of the SNP's broken pre-election promises, we will need Scotland's teachers to be willing to believe in another set of SNP pre-election promises.

We will need them to place their faith in politicians with a track record of exploiting the profession and failing to deliver on their commitments.

We will need them, against all the evidence of the past decade, to trust the SNP.

That, above all, is going to be a hard sell.

© Herald Scotland