What is it? It’s the smell of education, that unique blend of sweat, old dinners of the pre-cafeteria variety and fear.

The truth is that it’s never gone away since I crossed the threshold of St Mirin’s primary in August 1955, and, despite child-centred teaching methods, new reading schemes, 5-14 and a myriad of changes, including banning the belt - which had dispensed with your being welcomed into schools by a heidie leathering fearful latecomers, so lessening the smell of fear - it has either stayed the same or become higher still.

What is interesting is that school staff tend to be immune, perhaps just admitting to catching a whiff of what is to come when they walk back in on day one of the new term. But, arrive with a visitor outwith the education service, and it’s a certainty that they will mention the smell.

As one of our community cops, a lad who has seen more than a little action in his day, said to me as we walked in for a photocall with a group of primary sevens: “I feel as if I’m a wean back at school.”

That smell-triggered memory reflex may be part of the answer to the problem of why so many parents regress into pupil mode when coming to school to see teachers or the heidie. It may also explain why getting adults back into secondary schools took a while to be accepted when the former Strathclyde Region pioneered it in the 1980s.

I recall interviewing a mother at the now-demolished St Augustine’s Secondary in Glasgow, and asking her what she disliked most about coming back. “It’s that smell,” she laughed nervously. “It takes me right back to when I was here. They don’t still use the belt, do they?”

What is interesting is that schools in middle-class areas smell exactly like those in more socially deprived areas, although the incidence of washing by individual pupils may vary, together with a ider margin of individual variation. One of the greater and unresearched mysteries of Scottish education today, is why the smell quotient is not variable as a result.

It can be argued that secondaries do smell differently from primaries, where the special aroma generated by having children play in sock soles for gym in the communal dining area, immediately before lunch is served, adds to the piquancy.

Secondaries usually smell more intensely the further you explore them, with aromas as diverse as the science labs mixing with fumes from smokers’ corner, past the fast-food outlet, including the burger van at the gates, to the special scent of adolescent sweat hanging about the gym.

But there can be problems in individual classrooms, usually around third year, where that adolescent aroma, confined with blinds down and windows jammed shut because of capital shortfalls, can be overpowering as you attempt to deliver your talk to a media studies class about what a press officer does.

Maybe it’s the adolescent equi-valents of hot flushes, the special hum of boys’ sweaty feet, the deodorant sprayed directly on to shirt oxters after PE, known as a “Govan shower” in the greater Glasgow area, or the smell of bursting plooks and the lotions put on them. Whatever it is, you can’t help longing for one of those Victorian classrooms where the architects realised that pupils ponged and built roofs as high as possible to allow the fumes to rise and dissipate.

Many teachers I have met are conscious of the smelly world of work, and fight back with sprays and fresh air. A member of the directorate in one council I know has never shaken that off, and every socket in his room carries an electric fresh air dispenser, with the smell of sweet moorland replacing 3F last thing on a Friday, of smelly memory.

But nothing, nothing I can think of, can compete for sheer horror with the whiff of the boys’ toilets in a primary school.

You don’t have to enter, just walk past, and you will quickly see why teaching is not a profession to be sniffed at, as long as you turn your nose up as you enter its portals.