Sir – It is depressing and interesting to see the way we are repeatedly suckered into misinterpreting the data available on schools. The implicit assumption is that the position of a school in some kind of ranking can be treated as a measure of the quality of their educational provision.

In fact the differences between secondary schools are known to depend on the prior achievement of children.

Surely the relevant question for a parent is whether, given the characteristics of their child, any particular school can be expected to produce better subsequent achievements than any other chosen school.

One relevant question for parents is — why do so many schools that have appeared to increase the percentage of their pupils achieving 5+ A-C grades have the lowest percentage achieving A-G grades overall? Are these schools selectively ignoring the learning needs of many to benefit the few?

The current system is an incentive for a school to discourage pupils from taking “hard” subjects because they fear depressing the proportion achieving a ‘C+’ grade; such schools are also tempted to concentrate excessively on “borderline” pupils who might just scrape the C grade which counts towards the school’s score, at the expense of those striving for what should still be laudable achievements.

For those that hold on to a principle of choice (and competition) as being an important driver of quality in schools then surely what is really required is a predicted school effect some six years beyond the current data, but your readers might like to know that the correlation between school effects for different cohorts of children taking our current exams is actually very low. Support your local school.

Frank Newhofer, Oxford