The C/D borderline is hard to erase from a headteacher’s consciousness. The arbitrary accountability measure to which we were so wedded - five A*-C GCSE grades, including English and maths - has, on reflection, influenced too many of my decisions for the past decade.

The thing is, can you blame me? Our school’s reputation - and my job security - has largely rested upon the percentage of our students attaining grade Cs or better in their English and maths GCSE examinations.

So what if student X came to us with level 5a in her key stage 2 Sats but only attained 10 GCSE grade Bs five years later? She was over the key accountability threshold. She may not have made the progress predicted, but she was in my five A*-C bag. Job done.

In days of old when the GCSE mocks spreadsheet landed on my desk in the first week of January, it was ranked by the number of A*-C grades, including English and maths. Those who were over the accountability threshold received little attention. The worst performers were our lowest starters and our students with SEND. We focused the bulk of our attention on the 30 or so students who sat around the C/D borderline; after school on Tuesdays was reserved for English language interventions and on Wednesdays, it was for extra mathematics.

Wasted effort

Oh, how those 30 loved being made to stay behind when they were tired and fed up, to be taught by teachers who were fed up and tired.

The benefits were minimal. Truants had to be followed up and punished. The whole process drained everyone. Every protagonist dutifully played their role in a performance which was largely ineffectual.

As Churchill might have said, never has such a huge effort been made by so many for so little impact.

But last week, when this year’s GCSE mock data was presented to me, it was ranked by the students’ residual score against their FFT Attainment 8 estimates.

Student X, who, in the bad old days of five A*-C GCSE grades, including English and maths, would have been flailing around in the bottom row, was ranked number 72 out of 233 students. A couple of our students with SEND sat proudly in this year’s top 30.

We are going to help others who want our help and will be grateful for it 

And in last place, number 233 out of 233, was a student who had 100 per cent attendance, had great effort scores, had a modal FFT GCSE grade estimate of A*, and was an average, per subject, of nearly three GCSE grades below her estimates. She is astrologically predestined to attain five A*-C GCSE grades, including English and maths, but is a progress disaster waiting to happen. She is a delightful young person who, in the past, might well have left our school with life chances half of what they might have been if we’d noticed her at all.

And it’s worth noting, if you haven’t already, that a high starter missing a top grade has a bigger impact than a low starter missing a bottom grade. Under the interim GCSE system for summer 2017, we will be more heavily punished for an A* grade target student attaining a C (4-8.5 = -4.5) than we will for a D grade target student getting a G (1-3 = -2).

I can’t believe that this is a deliberate incentive from government for headteachers to improve attainment at the top end.

The whole experience has made me question everything about my past 13 years of headship. How was I so blind to what was happening? How many past students hardly registered on our radar as we tracked their performance? How many left the school where I was headteacher with a set of examination results which could have been so much more impressive?

Is it my fault, or is it ultimately the Labour government that must take responsibility for the idiocy of my response to the incentives that it set?

Big gains

So, what do we do now, in the four months left before the GCSEs begin? Keep pouring our limited resources into supporting the C/D borderliners and the small number of chronically disaffected, with little to show for it in terms of improvement between now and May?

Or do we spread our efforts more widely and help those who have high Attainment 8 estimates but who aren’t quite getting it; those who, with a little help, would make significant, rapid progress?

In the end, we do both, don’t we? But I am now inclined to think harder about where we draw the line if we are making more effort than the student we are endeavouring to help. I will be more judicious in targeting our efforts to increase our students’ progress. It’s all about looking at student performance through a Progress 8 lens. It will change your (professional) life.

Post Script: back in November, we had a student who chose to have a lie-in rather than come in for a practical examination. We sent two colleagues on a 30-mile round trip to get him out of bed and drive him into school. He took the exam.

I met with the same student last week for a “tough love” meeting. He began by triumphantly declaring how little he cared about his studies and his future. I let him finish and then said, “Well, I’ll let you into a secret. If you don’t care, then nor do I. We are stopping chasing you up and we will do the minimum for you between now and the exams. We are going to help others who want our help and who will be grateful for it.” His face was a proverbial picture.

But it worked. When I popped into his geography GCSE class an hour later, his face was flushed red with the effort he was making.

John Tomsett is headteacher at Huntington School in York. He is also a member of the Head’s Roundtable. He tweets @johntomsett