Our source was unable to discover which firm had won the contract - "it was one of those massive firms that parasite onto public sectors contracts, like Serco or Capita, but neither of those two - I can't remember and they'd erased their logo from the paperwork by the time it reached me, once they realised the project was tanking. They'd moved on to a new DWP contract removing the long-term unemployed from the voting register by then."

The reason the formula has not been applied is obvious upon closer examination of the maths involved. Here is the formula, explained by our NAO statistician:

"It looks complex but let me break it down for you. The sideways M letters are sigmas - you add things up. c is the number of curriculum change initiatives - numbered as y ('why bother') - you add all them up from the first day of government to a maximum level of d (for 'derision') - gauged by how many of the population think, inexplicably given that they don't think this about doctors or nurses, that they could do your job better than you. To reduce this slightly, you divide this by h times t where h is the holiday length and t the relatively early time in the day teachers are said to finish, so the top-left sigma is about stress caused by managers and parents and what little respite teachers get from that. You could remember the 'ht' as standing for half-term if you like, except most teachers just spend them ill, recovering barely in time for the next Monday. The ht divider used to balance this proportion of the graph out but in the last decade, and particularly under this government, this part's become top-heavy: the EBacc is messing with the curriculum and the right-wing press has ramped up the we-hate-those-lazy-teachers rhetoric from the 1980s again, and then Gove is trying to abolish the summer holiday too. Plus anyone in the industry knows nobody goes home at half three anyway, so this is the first big stress block.

"The second sigma function is based on stress caused by children. It sums up i - people presumed at first that it stands for children's usual self-centredness, or the 'x' for the zero initiative they regularly show, but actually this function is a measure of how much they use their iPhones instead of doing what they're supposed to - from a value of zero to f, where f is how many times in the average lesson they try to check their Facebook page. This can be divided by w, or the number of bottles of wine teachers are provided with at the end of term. Obviously that divider makes this part of the score very favourable for staff in independent schools, whereas it is often as low as zero for state school teachers, meaning that the child-caused stress figure is divided by zero, producing a level of infinity for stress in this sigma function for teachers in schools of the ungrateful poor.

"Next you add together those two sets of data and multiply them by the large E divided by the small r. The E stands for the ego of your particular headteacher and acts as a multiplier for how much stress comes down to classroom teachers. The nearest thing we have to data from the 1980s suggested that headteachers protected their staff from stress and stupid central initiatives because they remembered what it was like in the classroom but now we have NPQH to develop a sense in headteachers that they're altogether different in kind from teachers, they're a master race who rise to the top inevitably and owe nothing to their erstwhile colleagues. The really important thing, they now realise, is for them to make to it to being Chief Exec of a profit-making academy chain earning a quarter of a million a year so they need never step in a classroom again. You divide this by r - for remuneration of normal teachers, which is obviously falling after years of consecutive pay freezes. Remuneration was slightly higher in some academies than unconverted schools, but this effect is massively outweighed by the Ego rating of heads of academies, who pretty much all think themselves Plato.

"A helpful mnemonic to remember this part of the teacher stress equation is that E/r is like 'Emergency Room', because by now the patient is all but dead on the table."

Next this total amount of stress, for causes from above and below and balanced with any possible benefits, made specific to your context, is divided by a multiplier called 'ao/b'. Our statistician explains: "This is three factors considered together: a is for attendance - we don't know why that's in there, but apparently it has to be included in all school data now, no matter how relevant or otherwise; o is 'opportunity index', a measure of how wealthy an area a school is in, sometimes also called the 'offensiveness index' because we measure it by how many minutes a teacher can go for without being verbally abused in a way most other professionals never have to suffer. In many independent schools this can be months at a time, whereas in inner-city schools it's usually a fraction of a minute. This produces a really low divider score, raising the overall stress level coming out of the equation. You multiply the attendance by how much respite teachers get and then divide it by b, which is 'bare-faced cheek.' This is ascertained by reading the Education Secretary's recent pronouncements, in which a millionaire educated at a thirty-thousand-pound-a-year school with a pupil / teacher ratio of 8:1 and which sends more students to Oxbridge than the whole UK Free School Meals population lectures the working classes on how it's their fault they've failed to penetrate the inbred network of privilege and favour that forms the closed upper echelons of UK society. In short - the more Gove opens his mouth, the higher teacher stress levels rise.

"You can probably remember these variables because by calling them 'aob' we've basically chucked everything else we can into the equation, just so it's really hard to calculate, is even more non-specific, and wastes another load of time you can't spare. Best of luck working it out. Apparently they were going to call this denominator the 'Gove Fantasy Index' but that got vetoed early on."

So far so complex. Many teachers will have been trying to calculate their own stress levels using the calculus so far; but if you're pleasantly surprised by how low it is, read on and brace yourself. The real problem with the data recently, has been the next step - you need to put the number arrived-at so far through the exponential 'bull' factor. The best way to explain this is to hand back to our statistician. "Oh, the bull - that's easy to explain. This stands for 'beating up on lead learners' and is a measure of how much abuse comes out of Wilshaws's mouth, directed at teachers. If you know anything about maths you realise how rapidly exponential rise can push the final number up - and this is where Wilshaw has made a real impact. He's had nothing nice to say about teachers either during his long public soundbite audition for the post, nor for the time he's been in post. He's actually not been in the role long, although for most teachers it will feel like he's been there an eternity. Apparently in the design of the equation consideration was given to multiplying the bull by an 'mp' factor - not for 'Member of Parliament' but for 'Michael Palin' effect for how amusingly ironic it is when Wilshaw bangs on about teachers not feeling stress then contradictorily uses his own experience as a teacher as a comparative reference. It reminds people of the 'When I was a lad, we were so poor we lived in a hole in the road' sketch of Monty Python fame, basically."

We asked one teacher in Walthamstow what the difference was between Wilshaw and his predecessor Christine Gilbert. "It's like swapping matron from the

*Carry On*films for Voldemort," she said, turning pale. "She was just a mean and humourless old bitch - although it's funny looking at her hypocrisy now trying to defend the profession - but he's a force of unmitigated evil, aiming for universal domination and the destruction of all that is good and true. OFSTED Inspectors are basically the Dementors from

*Harry Potter*, let's face it. I wouldn't mind half a chance to f***ing

*Expelliarmus*him."

There is one final tiny positive tweak in the calculation. Teachers will be half-heartedly reassured that a (small) deduction can be made from the now-astronomical stress figure produced by the calculus so far. Over once again to our statistician:

"Notice the small-font 'ps' at the end. You take the value of a teacher's pension for p, and the sense of solidarity with colleagues whose integrity and ethics are also under constant assault by those meant to champion and represent them - and multiply them together to get 'ps', and take this away from the result so far. Whilst solidarity is at last rising again, that's being more than offset by the fall in the value of pensions.

"Of course, as deductions to stress go, by then it's like Palestinian children chucking stones at tanks, it's that futile and irrelevant an impact. So 'ps' in small font seems quite fitting because it's a trivial afterthought, let's face it."

It appears that the reason for burying the formula - assembled expensively in the private sector for a budget of around four million pounds (enough to run a medium-sized comprehensive school for a year) - is political: not only did data testing of the formula on teachers across multiple schools produce results in all cases likely to end in the DfE being sued for constructive dismissal, the highest results of all were in Gove's newly-formed academies.

"It was a nightmare" reports our source. "The stress levels coming out of the model were above all maximum health and safety limits set by EU law. Gove went mental. Somebody senior said the government wanted us to bury it until we can pull out of the EU Social Chapter - there was something about how, after that, we can screw teachers and the rest of the workforce all we like, but until then it might leave the government liable for large payouts. Worse yet, it turned out that neither the Education Secretary nor the Head of Ofsted scored anything like as highly for stress as the mean figure for year 5 teachers in urban schools. That would have looked really embarrassing, so I guess that's why they canned it."

The private sector contractor allegedly offered to look again at the model, but their eight million pound redraft fee was considered unreachable, with the D of E already having closed two county support centres for children with learning disabilities so that the private sector firm could put in the six hours' work needed to draft the original formula. "Plus," adds the civil servant, "it was difficult to reach them again after the problem arose. We could only get through to voicemail and a message saying they were on their way to the bank. There was quite a lot of laughter in the background."

This blog approached the teacher unions for comment in response. NASUWT sighed then put down the phone, the ATL representative just wept for twenty minutes, and the NUT phone line went quiet, followed by sounds of weaponry being armed faintly in the background. We'll keep you updated on further developments. At an hour-long INSET to explain the new calculus at one rural school in the North-West, one sparky NQT asked whether it could integrated with SIMS for export to a marksheet, while seven of twelve heads of department exhaustedly indicated they didn't understand the data anyway.