Worrying about how students’ exam papers would be marked never used to keep me awake at night. But it does now I’ve been involved in the marking process as an A-level history examiner this summer.

The marking experience turned out to be surprising. It surprised me that one student thought they could boost their grade by including their phone number and what is most politely termed “an invitation”. It surprised me that another student decided it would be best to write their entire five-and-a-half-page essay in block capitals. But what surprised me most was the loss of faith I experienced.

The first shock came on the training day for all examiners. I had naively assumed that there would be some kind of consensus about what made a good essay. Not so. In fact, the level of disagreement was staggering. Essays considered worthy of full marks by some were dismissed as D-grade work by others. But perhaps differences of opinion were to be expected at this stage and all marking would become consistent after a few hours’ training. Perhaps.

And I had not expected to have to mark papers on topics I had never taught and had no knowledge of. I had assumed that to mark A-level essays it would be necessary to have some idea of whether what a candidate was saying was true, but when I pointed this out I was told that the situation used to be a lot worse. No worries there, then.

At least once the marking started I knew I wouldn’t be able to go far wrong. After all, I had read that about 4 per cent of the papers I marked would be secret test scripts used to check the accuracy of marking. I would not be told which these scripts were, and if the mark I awarded them differed significantly from the “correct” mark I would have to explain myself. Foolproof, right? Wrong.

The problem with these “secret test scripts” was that every examiner had seen them before - they were the scripts used during the initial training day. So every time a familiar script popped up, a quick look at the training notes was all it took to see exactly what mark should be awarded.

This fails to even touch on the problems inherent in marking a high volume of papers under tight deadlines. One hopes that this does not lead to mistakes. One hopes that examiners are able to remain consistent. One is clearly an optimist.

The writer is a secondary school teacher from the West Midlands. To tell us what keeps you awake at night, email david.marley@tes.co.uk.