Standardised age scores: what an SAS of 121 means

The number on your child’s result letter is a position, not a mark. It compares your child with everyone who sat the same paper, adjusted for their age on the day. It is not a percentage, and it is not a mark out of anything. On its own it does not tell you whether your child has done well.

What makes it mean something is the scale it sits on and the group it was measured against. Buckinghamshire, for example, publishes a single figure and says plainly that a score of 121 or above qualifies for a grammar school. In Essex, that figure is not one any family would ever be shown, because the total there is built out of different parts. Same idea, different arithmetic, and no way to read one against the other.

What is the number actually measuring?

Standardisation is a piece of arithmetic done after the test, not a judgement made during it. The provider takes every raw mark, works out how the whole group did, and rewrites each mark as a position in that group.

The Consortium of Selective Schools in Essex publishes its version in full, which is unusual and useful. Each paper is rewritten so that the average is 100 and the standard deviation is 15, using the mean and the spread of the children who actually sat that paper that year, and how the CSSE test works across all ten Essex schools sets out the rest of that format.

That design has two consequences.

The first is that the score moves with the cohort. A strong year makes a given raw mark look less impressive and a weak year does the opposite, because the comparison group is the one that turned up on the day. This is not a flaw in the design, it is the design: the school wants to know where your child sits among the children it is choosing between.

The second is that the score is only as meaningful as the group it was measured against, and different areas anchor their scales to different things. That is where most of the confusion parents carry into results week comes from. If you would rather see a real spread than read a description of one, a full year of Kent Test results sets it out candidate by candidate.

What does the number tell you, and what does it not?

Here is the arithmetic a results letter never shows. Our own scoring engine assumes the textbook shape, a normal curve with a mean of 100 and a standard deviation of 15. On that curve a score of 121 sits at about the 92nd percentile, so roughly eight children in every hundred would be at or above it.

Now put that beside what Buckinghamshire publishes. The council says a child’s standardised score will be between 60 and 170, and that it expects about 37 per cent of children to reach 121 or more.

Both statements are true, and they are not in conflict. They describe different distributions: ours is what a textbook curve does, and the council’s is what its own scale and its own cohort actually produce. A standardised score is a comparison, and until you know what it is a comparison with, the number on its own is a label rather than a measurement. We have sat with parents who spent a fortnight setting a figure from one county against a figure from another, and the two were never on speaking terms.

Why do different areas report such different numbers?

Where	How the total is built	The number a family sees
Buckinghamshire	Verbal, mathematical and non-verbal, weighted 50 / 25 / 25	A single score between 60 and 170, qualifying at 121
Bexley	Verbal, numerical and non-verbal, weighted 50 / 25 / 25	A weighted total averaging 200, with about two thirds between 170 and 230
Essex, CSSE schools	English and maths, weighted 1:1, then multiplied by 1.5	A total where an exactly average candidate born on the reference date scores 300

Buckinghamshire and Bexley weight their three parts in exactly the same proportions and still hand parents numbers on scales that cannot be read against each other. Nothing shows more clearly that the figure on the letter is a presentation choice as much as a measurement. If you want to see how a real school states its own standard, the records for Dr Challoner’s Grammar School and Colchester Royal Grammar School show two of these scales side by side, each with the date we last checked it. Which scale applies to your child depends on which test they sit, so settle which test your child will actually sit early, because it decides everything else.

What does the age adjustment actually do?

The word “age” in standardised age score is doing real work. A child born in late August sits the same paper as a child born the previous September who has had nearly a full extra year of school. The adjustment exists so that being young in the year group is not a standing disadvantage in every selective test in the country.

Most providers do not publish the size of the adjustment. The Essex consortium does, and it is small enough to be reassuring and large enough to matter.

Ana and Ben both sit the CSSE 11+ for 2025 entry and both are exactly average on both papers, so each is standardised to 100 in English and 100 in maths. Ana was born on 1 September 2013, the reference date the consortium uses. Ben was born on 31 August 2014. What total does each of them end up with?

The usual wrong route

Almost everyone says the totals must be identical, because the marks are identical, and that any difference would be a favour done to the younger child. Neither is right. The difference is published arithmetic, applied to every candidate before anyone looks at a name.

The method

1. Each paper is standardised to a mean of 100 and a standard deviation of 15, so an exactly average paper scores 100.
2. The consortium’s total is 1.5 times the sum of the two standardised papers. For Ana, born on the reference date, that is 1.5 x (100 + 100) = 300.
3. “Days younger” is the child’s date of birth minus 1 September 2013. For Ben, born on 31 August 2014, that is 364 days.
4. For 2025 entry the published English age adjustment was 0.016207376 per day younger, and the maths adjustment was zero, because the consortium’s own test found no significant age effect in maths that year. Ben’s English score becomes 100 + (364 x 0.016207376) = 105.9.
5. Ben’s total is 1.5 x (100 + 105.9) = 308.8, which is about 309.
6. The gap is a little under nine points, on a scale where an average candidate born at the start of the year scores 300.

The following year’s report applied an adjustment to both papers rather than one, so the size of this gap is recalculated every year and is not a constant you can look up.

Answer: Ana 300, Ben about 309In the paper: Two minutes with a calculator.

Our own reporting works the same way, on a smaller scale and with our own numbers: the engine that produces the score on a PlusProgress mock adds 0.18 of a point for each month a child is younger than the reference age, which is a little over two points across a full school year. The direction is the same everywhere. The size is not, and nobody should quote you one without saying whose scale it belongs to.

Can a practice percentage be turned into a score?

This is the part that disappoints people, so we will be blunt. A percentage from a paper done at the kitchen table cannot be converted into a standardised score. Not roughly, not with a chart, not with a calculator that promises otherwise.

The reason is in the arithmetic above: standardisation needs a mean and a standard deviation, and those come from the children who sat that particular paper. At home there is no cohort. There is one child, one paper, and no way of knowing how several thousand others would have done on it.

What a percentage does tell you is direction of travel. The same child, on the same kind of paper, under the same conditions, scoring better in February than in November, is real information and it is the information worth having. Our own standardised scores explainer and calculator shows the same arithmetic as an illustration and deliberately gives a band rather than a single confident number, for exactly this reason.

How should you read the result letter?

When the letter arrives, resist the number for sixty seconds and read the rest first: which papers were sat, what scale each one is reported on, what standard the school or authority set this year, and only then what your child was given. Reading the number first is what turns an ordinary piece of information into a bad evening.

If the score is below the standard, the next question is procedural rather than academic, and what happens on results day, and how waiting lists and appeals work covers it properly. If you are earlier in the process than that, when to start preparing for the 11+ answers the question parents ask first, and the shape of the scoring in one of the largest selective areas is set out in how the Kent Test is scored and reported.

What should you do next for your child?

Three practical things follow.

• Prepare for the paper, not for the scale. Nothing you do at home changes how standardisation works, and everything you do at home changes the raw mark that goes into it.
• Treat a summer birthday as a fact the scoring already knows about rather than a headwind to worry at. In at least one consortium the allowance is published, and it is applied automatically.
• Read every score next to its own scale and its own school. A number copied from a forum post about another county is not evidence about your child.

Common questions

Is 121 a good score?

It depends entirely on the scale it sits on and the school that set it. In Buckinghamshire 121 is the published qualifying score for a grammar school place, and the council expects about 37 per cent of children who sit the test to reach it. On a scale where the total runs into the hundreds, 121 is not a comparable figure at all .

Can I convert a practice percentage into a standardised age score?

No, and anyone offering an exact conversion is guessing. Standardisation is done against the children who actually sat that paper, using a mean and a standard deviation the provider calculates after the event. At your kitchen table there is no cohort to standardise against.

Does my child’s birth month really change the score?

Yes, and the size of the change is sometimes published. For 2025 entry the Essex consortium added 0.016207376 of a standardised English point for every day a child was younger than 1 September 2013, which is close to nine points of final total for a child born at the very end of the school year .

Why do two schools quote such different numbers?

Because they are counting different things. Buckinghamshire reports a single weighted score that qualifies at 121 ; Bexley reports a total that averages 200 ; the Essex consortium reports a total where an average candidate born on the reference date scores 300 . Always read the scale before the number.