Deja vu? Last week an education adviser, Sir Cyril Taylor, has revisited a classic piece of scaremongering to whip up publicity (sorry, that should read “has made a valuable, balanced and thoughtful contribution to the education debate”), namely that 17,000 teachers are sub-standard. I would have dismissed this little piece of news as isolated ramblings except that a headteacher I know was recently told by an inspector, after he had observed one of his outstanding teachers, that “What this school needs is for all the teachers to be like that.”

But of course! All headteachers will now realise that they can sack all their staff tomorrow except for their two best teachers and put an advert in the paper for 10 others just like them. Have the England selectors heard about this breakthrough? Get rid of all of the England cricket team apart from Kevin Pietersen and then recruit another 10 players exactly like him. Brilliant!

What is a “sub-standard” teacher anyway? Surely it depends on circumstances and the subject observed. During my first inspection many years ago, my headteacher was kind enough to steer inspectors away from my music lesson. When forced to teach music, I have tried my best but it usually ends with several children in tears, a maraca fight and any adult observer having to seek counselling for post-traumatic stress disorder. I’m sure, despite being a reasonably competent teacher, I would have scored a 7 on the old 1 to 7 scale - and even though the scale is now only 1 to 4, I bet if I still taught music I’d still get a 7.

Of course, music is relatively unimportant. I feel safe writing that because most music co-ordinators never get round to browsing The TES; they are too busy at break wringing their hands and shouting in a deranged manner at the recorder orchestra. It’s more of a concern when teachers have a mental block with a core subject. Someone holding forth on the evils of Darwinism in the staffroom then heading off to teach science might be considered a worry.

One of my colleagues once triumphantly appeared at my classroom door with a set of Unifix cubes and announced that she had just discovered that the formula for the volume of a cuboid didn’t work. She seemed convinced that the next day’s papers would be full of stories of a Year 4 teacher who had overturned 10,000 years of mathematical orthodoxy. Except that she was holding up a sort of 3D “L” shape. Not a cuboid. A letter “L”. As in “Lunatic”.

So how does the grading of teachers work? Apparently Ofsted inspectors are now unable to give a school good grades for teaching, despite what they observe, if the school’s national test results are bad. A masterstroke. Just the encouragement we need to bring top teachers to schools in the worst areas.

The positive side of this story? Politicians might only get inspected once every four years, but at least when we give them a failing grade they have to go.

More from Henry in a fortnight.