It is dangerous to flaunt your free periods. There may be someone, somewhere out there, monitoring everything you do.
At a time when the rest of the world seems to be spending most of its waking hours discussing what can be taken away from teachers - the summer holidays, incremental pay increases - the free period could soon be on the hit list.
It was seeing a letter in a local newspaper that put me on my guard. The letter, signed by an unnamed "retired professional", described how a teacher - "a well-dressed woman, possibly in her fifties" - was spotted in a women's dress shop in the middle of the morning.
She was heard to say: "I had better get back and do some more teaching - how boring."
The letter writer commented: "I suppose she will find it rather 'boring' when spending her salary at the end of the month, finds housework 'boring' and, as with many teachers I have known, is completely disorganised at home, which can onlybe reflected in her teaching standards.
"If, like other mortals, she had a real job, occupation or profession, she would not be able to 'swan' around dress shops in time which, after all, she is being paid for by the tax payer.
"The real world, madam, is 9am to 5.30pm or such like, but then teachers have never been there."
I began to wonder why the letter writer had adopted a sobriquet. Surely anyone able to express his views so impressively would not be scared to reveal his identity. Perhaps he was really a government agent.
If he really was a "retired professional", he must simply have forgotten some of the perks enjoyed by people who live in the "real world": the long lunches, the company cars, the freebies to exotic locations, the private health schemes, the expenses and the hefty pay packets. That was just the kind of slip of memory that anyone could make.
But let us not be too ready to find fault. Let us praise him for his achievement - he had found a teacher in a dress shop!
And before they take the free periods away from us, let us try to learn a lesson from this incident. When the bell goes for that longed-for moment of calm, we should avoid calling out, "I'm free!", like John Inman in television's Are You Being Served? Instead, we should celebrate privately and - like Chaucer's Sergeant of the Law in The Canterbury Tales - try to seem busier than we really are.
Peter King teaches English at Wisbech Grammar School, Cambridgeshire.