Candidates have five minutes left,” said the invigilator as I frantically scribbled my final answer. “Your response will be assessed according to the quality of the sentence construction, grammar and spelling” - or so the rubric said. I could scarcely read some of my own writing, still less pass it off as accurate and well-constructed English. And so, after a 26-year gap from public examinations, I waited for my AS-level critical thinking script to be collected and assessed alongside those of my students at King Henry VIII school, Coventry.

I’d decided in January that I would enter the exam along with the Year 13 group I’d been teaching. My group was flagging. “Why do we have to do this, Sir?” and “Are you sure my universities will take any notice of this?” were questions ringing in my ears. Sound familiar?

I also wanted to challenge the idea that AS-levels are easy, and critical thinking, examined by the OCR board, is a new(ish) and challenging subject that university admissions tutors would do well to consider. Besides, schools are about learning, and the example “from the top” is important.

Essentially, critical thinking is learning to analyse and synthesise arguments, evaluate the quality of reasoning and spot weaknesses, contradictions and assumptions. Inevitably, it promotes awareness of current affairs and politics because it is around these that the subject matter is generated.

I’m sure the skills that critical thinkers have to develop are transferable to other subjects and should improve students’ articulacy and confidence in, say, a formal interview. Inevitably, these benefits are not always evident to the student, who may rail at yet another examination course and yet another set of hoops to jump through.

I had kept my entry secret but eventually couldn’t resist sharing it with the group. I wanted us to work together and saw the ritual of the exam room as part of that. In the few days leading up to the exam. I found myself setting aside small parcels of time for revision, then wondering if it was any help. I had learned various meanings and definitions, but could I find an excuse to use them in the exam? Could I even remember my candidate number? And so the day came: I mixed awkwardly with my students outside the exam hall. Nobody likes to fail, least of all me.

Two 90-minute papers followed, separated only by a five-minute gap. I’d not worked so intensively for some time, and certainly not against the clock. Paper 1 had 28 compulsory questions in which candidates had to assess the assumptions, flaws, moral principles and weaknesses of given evidence. Topics ranged from human cloning to organic fish farming, from psychoanalysis to bungee jumping. Paper 2 had three compulsory questions, all requiring extended writing. We had to critically evaluate passages of prose describing a dispute over a football match, the pros and cons of mobile phones and the benefits of English becoming a world-wide common language.

By the end I was exhausted. I was disappointed, too, at the non-appearance of carefully revised “definitions” and at my failure to complete all the answers in time. Then there were the interruptions to concentration caused by extraneous noise: the scraping chair, the cough, the squeaking shoe of the invigilator. Never underestimate the pressures of concentrating fully for three hours.

How have I done as a critical thinker? Well, I hope I’ll get a B grade; I doubt I have managed an A, although at least one of my students should do. Securing a mark of 80 per cent is no easy task. I feel irritated at the popular view that standards are falling and that getting an A grade is easy. This was not an easy exam and I would like to see some university admissions tutors take the same papers under the same conditions. Then they might appreciate the value of critical thinking in particular, and the pressures on AS students in general.

What resources have I drawn on? The onus certainly falls on the teacher, or in our case a group of six staff from various departments pooling our ideas. Newspaper articles - contrasting arguments on the same topic taken from several papers - television debates on BBC’s Question Time and Newsnight, radio’s Today in Parliament, and phone-ins. The medium is immaterial as long as the arguments are constructed clearly, or not. I think all of us, teachers and learners, have become more critical and more used to thinking. I have a vivid memory of my own university tutor (physics) saying that what he really wanted was undergraduates who could think. Not surprising, but interesting that he considered it necessary to say so.

And so to results day next week. Of course my thoughts will be on my students’ results, hoping they have achieved the grades they need and deserve. And, if my own grade is a disappointment, there’s always another chance next summerI George Fisher is headteacher of King Henry VIII school, Coventry, a mixed independent school with 1,100 pupils aged seven to 18.