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Every school in England publishes its exam results. And every parent trying to choose a school ends up looking at those results, comparing percentages, checking where a school sits in the county tables, trying to work out whether the numbers are good.
Here's the problem: the numbers are often measuring the wrong thing.
Results tables measure absolute outcomes. They tell you what grades pupils achieved. They don't tell you how much better those pupils did than they would have done somewhere else, which is, arguably, the only question that actually matters when you're choosing where to educate your child.
That gap is what value-added measures. And once you understand it, you can't quite look at league tables the same way again.
What Value-Added Actually Measures
Value-added is an educational performance metric that compares a pupil's outcomes at the end of a course with what would have been statistically predicted based on their prior attainment.
In plain terms: if a child enters Year 7 with test scores that suggest they're likely to achieve a grade 5 in GCSE Maths, and they leave with a 7, the school has added value. If they leave with a 4, the school has subtracted value. The question is not what grade they got, it's whether they got more or less than they were expected to.
Schools with high raw results often achieve them partly because they start with more academically able pupils. A school in a prosperous area, or one that selects heavily, will naturally produce higher grades but that doesn't necessarily mean it is a better school. It may simply be starting with a different intake.
Value-added strips away the intake advantage. It asks: given where these children started, how much did this school move them?
Why League Tables Can Be Misleading
This is not a cynical argument. It is a statistical one.
Consider two hypothetical schools:
School A achieves 80% of pupils at grade 7 or above in English. It is highly selective and draws pupils from prep schools across the south-west. Its intake includes many children who would have achieved grade 6 or 7 regardless of where they were educated.
School B achieves 60% of pupils at grade 7 or above in English. Its intake is mixed, some children from prep school backgrounds, others from state primaries, some with particular learning needs. But its value-added score is significantly positive: the school has moved pupils substantially beyond what their starting point predicted.
In the league table, School A ranks higher. In terms of teaching quality, the picture is different.
This matters directly for families making school choices. If your child is starting from a strong position, a good prep school, a solid Year 6, then raw results tell you something useful. But the question you should also be asking is: what does this school do for the children who are working hard but not in the top set? Value-added is the closest thing to an answer.
How to Find Value-Added Data
In England, the Department for Education publishes value-added measures for secondary schools through its school performance tables at compare-school-performance.service.gov.uk. These use a standardised calculation based on Key Stage 2 results versus GCSE outcomes, expressed as a progress score.
A score of 0 means the school's pupils made exactly the progress predicted. A positive score means they made more progress than predicted. A negative score means less.
For independent schools, this data is not always published in the same format, independent schools are not required to submit to the same DfE tables. This means you may need to ask directly: what can you tell me about value-added at your school? A school that has invested in tracking this will have the data. One that hasn't asked the question probably hasn't been paying attention to it.
What the Question Really Reveals
When you ask a school about value-added, you're not just asking for a number. You're asking about the school's theory of education.
A school that can answer this question well has typically been doing the following:
Tracking individual pupils from entry. They know where each child started, not just where they ended up. They have baseline data from Year 7 or Year 9 entry, and they track progress against that baseline regularly.
Acting on the data. Tracking is only useful if it changes what teachers do. A school that uses its tracking data to identify pupils who are ahead of predicted progress and extend them, and pupils who are behind predicted progress, and support them, is using value-added thinking operationally, not just as a marketing metric.
Taking credit for the harder work. Pushing a child from a predicted 5 to an achieved 6 is, in many ways, more demanding than pushing a predicted 8 to an achieved 9. Schools that take this seriously will have programmes for the middle of the cohort, not just their high-fliers and their students with additional needs, because they know that's where the value-added story is actually written.
What This Means at Leweston
Leweston works with a broad cohort. Its intake includes children from prep school backgrounds, children from state primaries, international pupils, pupils with additional learning needs, and pupils who are outstanding in one area and average in another.
Within that breadth, the school's academic tracking is designed to measure what each child achieves relative to where they started. Teachers know which pupils are working above prediction and which are below. Heads of Year track this across subjects. The pastoral and academic systems are integrated, so a dip in one area triggers a conversation, not just a report.
This approach means that a child who arrives at Leweston predicted to achieve solid GCSE results will be supported to achieve those results. But it also means a child who arrives predicted to achieve more will be stretched to do so, not left to drift in the absence of challenge.
The school's class sizes make this kind of individual tracking realistic in a way that it is not in larger schools. A teacher who knows fifteen pupils in a class genuinely knows how each of them is working. A teacher managing thirty does not have the same access to individual progress, however talented they are.
The Question Worth Asking
When you visit a school, any school, add this to your list: how do you measure what your pupils achieve relative to where they started, and what do you do with that information?
The answer will tell you a great deal about whether the school is managing its high-ability intake or genuinely developing every child it teaches.
Ask us about our value-added - call 01963 211015 or visit leweston.co.uk to book a visit or speak to the team.
Leweston School is a co-educational independent day and boarding school in Sherborne, Dorset, for pupils aged 3 months to 18, offering Nursery, Pre-Prep, Prep, Senior and Sixth Form on a single campus.