It may seem a bit of a cliché to warn that school performance tables should be handled with care, but there are good reasons for doing so. The old headline measure of the proportion of pupils passing five or more GCSEs, including English and maths, at grades A* to C was arbitrary and unfair. It applied in exactly the same way to all schools regardless of their intake and circumstances. Schools which had a relatively high proportion of vulnerable children with low prior attainment, would inevitably find it more difficult to do well than schools with more advantaged, high-attaining intakes.

So, let’s be clear: the advent of Progress 8 as a headline measure of school performance is an improvement. It aims to capture the progress that pupils make from the end of Key Stage 2 to the end of Key Stage 4. In theory, it creates a level playing field which judges all schools in the same way, not on a fixed measure of attainment, but on the progress that their pupils make during their secondary school education.

However, and it is a significant however, Progress 8 is not perfect.

Its greatest strength is that the grades of every pupil count. The old system put schools under intense pressure to get as many pupils as possible over the C/D borderline. Progress 8 takes into account the grades of every child, not only those who are capable of achieving C grades.

Ironically, however, this has also proved to be its greatest weakness. A school’s Progress 8 score is an average of all its pupils’ scores. So, if a small number of pupils miss exams because of personal crises in their lives or serious illness, and therefore have significant negative scores, it can have a disproportionate effect on the school’s score. ASCL is aware of schools where this has happened and the issue has been raised by several headteachers at conferences we have held around the country.

It cannot be right that schools are being judged on circumstances outside their control and we are pressing the government to address this problem as a matter of urgency. We are particularly concerned that the pupils in question are those who are most vulnerable and in greatest need. This means that the schools with the greatest challenges may be, once again, the most likely to be unfairly represented in the performance tables.

So, cliché or not, yesterday’s performance tables must be handled with care.

The lesson is that no performance system has so far been devised that manages to provide a complete picture. Our message to parents is not to place too much reliance on performance tables and to look at the school in its entirety; its curriculum and culture and how well it will suit their child. We would advise them to visit the school rather than basing their decision entirely on a set of data.

For the government, it is not only the flaws with Progress 8 that must be tackled. The results published yesterday come against a national backdrop of a crisis in education funding and teacher supply, and schools deserve great credit for all that they have achieved in these extremely difficult circumstances.

The government must take urgent action to ensure that schools have these essential resources. It needs to make education a political priority and invest more in the system. And it needs to initiate a long-term strategy, working alongside the teaching profession, to improve teacher recruitment and retention. For many of us, these issues will be the measure of the government’s performance.

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