Why the Top 25% of Results Matter More Than the Average

A school's average exam result is dominated by which pupils it admits — its intake — not by how well it teaches. Selective schools admit strong pupils and therefore produce strong averages regardless of teaching quality; non-selective schools with excellent teaching are penalised in average-based comparisons because their intake spans a wider ability range. Looking at the top 25 per cent of each school's results — what the strongest pupils at any school actually achieve — corrects for this and lets selective and non-selective schools be compared fairly. It is the single most important shift a parent can make in interpreting UK private school results.

This is a supporting article within our pillar guide to UK private school exam results, and one of the intellectual foundations of the My Top Schools platform.

The problem with average grades

The average GCSE or A-Level grade at a school is the single most-quoted number in independent-school marketing and league tables. It is also one of the most systematically misleading numbers a parent can look at.

Why? Because the average is dominated by two things:

1. Which pupils the school admits (its intake).
2. How well the school teaches those pupils (its added value).

Of the two, intake dominates by far. If a school selects only the top 5 per cent of national ability, its average grade will be high — because the pupils are already high achievers when they arrive. If a school admits pupils from the top 40 per cent, its average will inevitably be lower — even if teaching is exceptional.

Comparing these two schools on their averages tells you almost nothing about teaching quality. It tells you about intake.

The mathematical explanation

Think about it as a simple thought experiment. Imagine 1,000 pupils across two schools:

School A admits the top 100 pupils by ability. School B admits pupils ranked 400 to 500 by ability. Both schools teach with equal effectiveness. When exams come, School A's average will be far higher than School B's — not because it teaches better, but because its pupils started stronger. The relative difference in average is entirely a difference in intake.

Now imagine both schools teach exceptionally well. Both intakes will achieve higher than they otherwise would have. But School A's average will still be higher. The average, on its own, cannot separate intake from teaching.

The top 25 per cent solution

One of the fairest solutions is to look not at each school's average, but at the top 25 per cent of its results. This is the strongest quarter of each school's cohort.

The logic:

1. Every school has a top 25 per cent — the strongest quarter of its year group.
2. At a selective school, the top 25 per cent are drawn from an already-selective intake.
3. At a non-selective school, the top 25 per cent are drawn from a broader intake — but they represent the strongest pupils at that school.
4. Comparing the top 25 per cent of both schools tells you what the strongest pupils at each school actually achieve.
5. If the top 25 per cent at a non-selective school achieves close to what the top 25 per cent at a selective school achieves, that is a much stronger signal of teaching quality than headline averages ever provide.

It also reveals something important: some non-selective schools are producing top-quartile outcomes as strong as selective schools' — and they never appear as highly in average-based rankings.

A worked example

Consider two hypothetical schools. School X is highly selective — it takes pupils from the top 5 per cent of ability nationally. School Y is a strong non-selective independent school, admitting pupils from the top 40 per cent.

In a typical year:

• School X: 88 per cent of grades at 9-7 at GCSE. Headline average: strong.
• School Y: 60 per cent of grades at 9-7 at GCSE. Headline average: significantly lower.

A league table places School X far above School Y.

But look at the top 25 per cent of each school's results:

• School X: top 25 per cent achieve 98 per cent 9-7. Very strong.
• School Y: top 25 per cent achieve 92 per cent 9-7. Also very strong.

The gap between the schools has closed almost completely. The strongest pupils at School Y are achieving results just below the strongest pupils at School X — despite the school starting from a much broader intake. This is a genuine signal of teaching quality that the average completely obscured.

Why the average matters less than you think

The average matters because most parents have been trained to look at it. But if you step back:

• Your child will not be the average of the school. They will be one specific pupil.
• What matters is what pupils like your child achieve — not the median.
• If your child is likely to be in the top 25 per cent, the top 25 per cent is the more relevant statistic.
• If your child is likely to be in the middle 50 per cent, the average is more relevant. But even then, understanding the top 25 per cent tells you the ceiling of what the school is producing.

The average, in isolation, tells you nothing about what specifically your child would achieve. The top 25 per cent tells you what the strongest pupils are capable of achieving at that school — which is a much more useful piece of information.

Where the top 25 per cent comes from

Some schools publish top 25 per cent (or top 10 per cent) figures directly. Others do not, but the data is often derivable from published grade distributions. In particular:

• Percentage of grades at 9-7 (GCSE) or A*/A (A-Level) is often given.
• Percentage at 9-8 or A* is sometimes given.
• From these, top 25 per cent-equivalent figures can often be estimated.

My Top Schools is built to present this comparison directly, so parents can filter and compare schools on top 25 per cent performance without having to derive it themselves.

Where the top 25 per cent has limits

The top 25 per cent is a genuine improvement over the average, but it is not a complete answer:

• It still depends on the ability of the strongest 25 per cent of pupils — which varies by intake.
• It does not tell you about the bottom of the cohort.
• It works best combined with value-added and subject-specific data.
• For pupils not in the top quartile, other metrics may matter more.

The point is not that the top 25 per cent is the only useful number. It is that the average, on its own, is a materially misleading number — and the top 25 per cent is one of the fairer alternatives.

How this shapes the MTS approach

My Top Schools was built with this framing at its centre. Our approach:

• Present top 25 per cent results where available.
• Combine with value-added and subject-specific data.
• Let parents filter schools by strengths and outcomes, not just by geography or league table position.
• Present schools transparently, allowing selective and non-selective schools to be compared fairly.

This is not a critique of selective schools — many are excellent, and the top 25 per cent comparison often confirms that. It is a critique of using average-based comparisons as the primary way of ranking schools that admit fundamentally different pupil populations.

What to do with this in practice

When looking at a school, ask specifically:

1. What proportion of your GCSE grades are at 9-7 and 9-8?
2. What proportion of your A-Level grades are A* and A*/A?
3. What do the top 25 per cent of your pupils typically achieve?
4. How does this compare to schools with similar intake?
5. What is your value-added?
6. What are your specific subject strengths?

A school confident in its teaching will answer these clearly. A school relying on intake may deflect.

Final thought

Comparing schools on average grades is like comparing runners on the height of their parents. It measures something real — but not the thing you actually want to know. The top 25 per cent of results tells you, much more reliably, what the strongest pupils at any school actually achieve. Combined with value-added, subject-specific data and honest school visits, it lets parents make genuinely informed decisions — not decisions distorted by intake.

My Top Schools helps parents find the right school for their child — with clear profiles, honest information, and search filters built around what really matters. Start your search.

Related reading

• UK private school exam results explained — The full pillar guide.
• Are private school league tables misleading? — The critique of average-based rankings.
• What is a value-added score in school results? — The complementary measure.
• How to compare private schools fairly — The wider comparison framework.
• How to choose the right private school — The pillar on choice.