Numeracy is the subject of much attention at the moment. So I did some sums. First, percentages. How much of our school’s budget goes on teaching staff? Seventy-five per cent? That seems high. Perhaps we’re employing too many people.

But let’s try a ratio. Check the number of pupils against the number of staff - 18:1. Well that’s not generous - far from it, according to PANDA Annex information (OFSTED’s performance and assessment chart which helps a school compare its performance with others nationally). It quotes an average of 16.4 to 17.4. So our mixed comprehensive in south-west England is actually employing fewer teachers than many schools of similar size in other places.

Of course, we employ people other than teachers - administrators, clerical staff, librarians, technicians, classroom and mealtime assistants, grounds staff, caretakers and cleaners. These boost the figure by 12 per cent, giving total staffing costs of 87 per cent of our budget.

Although we live some miles from London, we pay staff on national scales. So our teachers cost the same as equivalent groups in Brighton, Birmingham, Banbury and Basildon. The same will be broadly true of our non-teaching staff and, come to that, of our fuel bills, the books we buy and the amount we pay to the exam boards.

If most of the items on our school budget cost the same in Cardiff, Coventry, Corby or Crewe, surely similar size schools in other parts of the United Kingdom should have roughly comparable budgets.

Time for some comparative statistics. The PANDA Annex, page 32 - income per pupil for a secondary school without sixth forms that have been inspected. The lower quartile received pound;2,118 per pupil, the median figure was pound;2,264 and the upper quartile generated pound;2,454. Our figure for the same year? pound;2,011.

What are the implications for a school like ours with 1,200 pupils? If we had been funded at the lower quartile figure we would have received pound;120,000 more, at the median level pound;300,000 more and at the upper quartile figure pound;500,000 more.

Why is one group of 1,200 secondary pupils in one part of the UK worth pound;500,000 less than a similar group in another area when most of the costs associated with their education are similar?

Perhaps I’m innumerate. But the sums don’t seem to add up.

The author is principal of a mixed comprehensive school in south-west England