Careless mistakes in 11+ maths: why “slow down” doesn’t work

Your child keeps making silly mistakes in maths. They are losing marks through carelessness on questions you have watched them answer perfectly well at the kitchen table. And every article you find gives the same handful of tips: slow down, show your working, read the question twice, check your answers, write neatly, get more sleep — and eat blueberries or soaked almonds, because they are good for the memory.

That advice is not wrong. For a lot of children it is exactly right. They slow down, they check their work, and after a few weeks those mistakes stop happening.

For other children, nothing changes. They slow down. They check. And they still lose the same marks, on the same kinds of question, paper after paper.

If that is closer to your experience, there may be a simple reason for it, and it has nothing to do with how hard your child is trying.

Three quite different things can look identical on a marked paper. All three get called careless. Only one of them really is.

The first kind: a genuine careless slip

Your child knows how to do the question, and on this particular occasion they didn't. They wrote a 7 that later looked like a 1. They read the word "fewer" and their eye took in "more". Sit down with them calmly ten minutes later and they get it right without any help at all.

This is the kind of mistake those other articles advise about, and for this type of slip, their advice works well.

The second kind: mental maths that is not automatic yet

This one is easy to miss, and almost nothing written for parents mentions it. It does not affect every child. But where it is happening, none of the usual advice will touch it — and it is most often found in children who are otherwise doing well.

Some children are well ahead in maths. They can follow advanced reasoning in questions aimed at much older children. But the mental arithmetic underneath never became automatic. Adding 7 and 8, they might write 14. Or 16.

At home, they would work it out on their fingers, and get it right.

In an exam room they will not do that. Nobody wants to be seen counting on their fingers at ten years old, with other children on either side. So they don't. And then, needing an answer to something that is supposed to be easy, with the clock running and a room full of people who all seem to have finished it, they take the best guess they can. Sometimes the guess is right. Sometimes it is one or two out.

Everything after that is perfect. They take their 14 and do every remaining step of a hard question exactly right — and get the whole thing wrong.

This is why a child can do the maths at the kitchen table and lose the marks in the test. Same child, same knowledge. What changed is that at home they were allowed to count.

They are not being careless, and they have not misunderstood anything. The foundation was never automatic — and in a room full of other children, the workaround they use at home is not available to them.

Slowing down does not help here, because the arithmetic is not going to arrive however long they stare at it. Teaching the method does not help either, because they already have the method and are using it correctly. What helps is making the number bonds and tables automatic, so no workaround is needed at all.

The giveaway is easy to see once you look for it. The working is right. One arithmetic step inside it is wrong, and usually wrong by only one or two.

The third kind: a method learnt slightly wrong

Somewhere along the way your child has picked up an idea that isn't quite true, and they are now applying it carefully and consistently, every single time.

Perhaps they have come to believe that the word "of" always means multiply. Or that a longer decimal must be a bigger one — that 0.417 has to be more than 0.6, because it has more digits in it. Or that when a question says "share", it means share equally, even when it also says three to five.

A child in that position is not being careless at all. They are being careful about something that is wrong. And they will do it again next week — slowly, neatly, having checked their work twice.

Which is why slowing down sometimes makes no difference whatsoever. If the method itself has a fault in it, working more carefully only produces a tidier version of the same wrong answer.

How to tell which kind of mistake your child is making

The useful question, then, isn't "how do I get my child to be more careful?" It is "which of these three is actually happening?"

You can answer it with a paper they have already sat. You don't need anything from us to do it. It takes two looks.

First, look at the working, not the answer. Follow it line by line and find the exact step where it goes wrong.

If the method is completely right and a single piece of arithmetic inside it is wrong — usually out by only one or two — you have found the second kind. The thinking is sound and the foundation wobbled. More reasoning practice will not touch this. Ten minutes a day on number bonds and tables will.

Then, if the method itself is what went wrong, look for a second question that tests the same idea. Most papers ask the same thing two or three times over, once gently and once with more layers on top.

If they got that other one right, this was a one-off slip. They clearly know the method — they just didn't use it properly that once. Checking habits will help, and so will slowing down. The usual advice is the right advice.

If they got both wrong, carelessness is an unlikely explanation. It is far more likely they have learnt one step slightly wrong — and no amount of care will find it, because from where they are sitting nothing looks broken. Ten minutes teaching that one specific step will do more than another whole paper.

Two looks, one paper. It will usually tell you more than a term of extra practice.

Why the same mistake follows your child into every topic

The first and the third behave quite differently once you start watching for them.

A one-off slip happens most often when your child is short of time — usually near the end of the paper, on questions that were not difficult. It does not happen every time. It is worse when they are tired and better when they are fresh.

A method learnt wrong is different. It happens every time, and it does not only happen in one subject.

A child who takes a fraction of the wrong amount will do exactly the same thing when the question is about percentages. And again when it is about ratio. And again in the questions about charts and tables. On a school report that looks like four separate weaknesses in four different subjects. In fact it is one mistake, made in four different subjects.

That is why it is worth finding out exactly what your child has misunderstood. Teach that one thing, and they stop losing marks in all four subjects at once.

To make that easier, we built 2,000 11+ maths questions across 20 topics and tagged every single one with the mistake it is designed to catch. Below are a handful of them — a small sample, chosen because they show the same mistake crossing over from one topic into another.

One of the sections below will probably sound like your own child. That is the one to start with.

One thing to say before you do. Some of these misunderstandings are first met in Year 4 or earlier, and it is tempting to read the name of one and think my child is well past that. Very often they are — at that level.

A misunderstanding does not stay at the level where it was learnt. It hides inside harder and harder questions, and it is worth more marks each time.

A child who muddles pounds and pence is not going to be caught out by 75p plus £1.80. They will be caught three years later by rope priced per metre and bought by the centimetre, in a question worth three marks. Same misunderstanding, far better disguised — and this time it takes the working with it.

So the examples below are written at 11+ level, not at the level where the idea was first taught. Even if one of them looks like a question your child would get right, read the "spot it" line underneath anyway. That is where the giveaway usually is.

---

When the numbers aren't in the same language

The maths is done perfectly well. The trouble is that the two numbers were never the same kind of thing to begin with — metres and centimetres, pounds and pence. Nothing needs re-teaching here, which makes these the easiest marks on the paper to recover.

Money — pounds and pence collide · 4 of 20 topics Rope costs £2.40 a metre. Mia buys 75 cm. They write £180.00 — it is £1.80 Spot it: An answer that is out by a factor of a hundred, or a price with three digits after the point.

Ordering decimals · 2 of 20 topics Order, smallest first: 5⁄8 · 0.617 · 62% · 3⁄5 They write 0.617 largest — it is 5⁄8 largest Spot it: Ask them to write all four as decimals to three places before comparing anything.

When the question runs backwards

These catch confident children hardest. Question after question says "here is the whole — find part of it." Then one hands over the part and asks for the whole, and a child working from habit does the familiar thing.

Finding the whole from a part · 4 of 20 topics After a 15% discount a coat costs £102. What was the original price? They write £117.30 — it is £120 Spot it: They added a percentage to the number in the question instead of dividing by one.

Think of a number · 3 of 20 topics Multiply by 3, subtract 7, halve it — the result is 16. What was the number? They write 20.5 — it is 13 Spot it: Their working repeats the operations from the question instead of reversing them.

When "of what?" quietly changes

Somewhere in the middle of the question, the thing being measured changes — from the original amount to what is left of it, from a total to one share. Nothing announces the change, so your child carries on with the first one.

"Of the rest" · 4 of 20 topics Ravi spends 2⁄5 on a game, then 1⁄3 of what remains on a book. £24 is left. They write £45 — it is £60 Spot it: The amount left after the first step never appears anywhere in their working.

Sharing in a ratio · 4 of 20 topics £4,200 shared between three schools as 2 : 3 : 5. How much more does the largest get than the smallest? They write £2,100 — it is £1,260 Spot it: Check whether the number 10 — the total number of parts — appears anywhere on their page.

When the words hide the maths

The arithmetic is genuinely easy. Getting from an English sentence to a sum is not. One small word — each, altogether, at least — decides whether to add or multiply, and it is easy to read straight past.

Remainders in real life · 3 of 20 topics Eggs are packed in boxes of 12. How many boxes for 1,000 eggs? They write 83.3 — it is 84 Spot it: A decimal answer to a question about a whole number of physical things.

Counting the possibilities · 2 of 20 topics A menu has 4 starters, 6 mains and 3 puddings. How many different three-course meals? They write 13 — it is 72 Spot it: They added the three numbers. Ask how many meals there would be with just 2 starters and 3 mains.

---

How to stop careless mistakes: what to say instead of "be careful"

Not "be careful". It is the most-used sentence in 11 plus preparation, and it has never once told a child what to do.

Replace it with the one specific thing. "Before you work it out, say out loud what the fraction is a fraction of." Or "Check both numbers are in the same units before you start." Or "Read the last line of the question again — what is it actually asking you for?"

Each of those names the exact moment the mark is lost, and each is short enough for a child to remember while the clock is running. "Be careful" is neither.

And if it turns out to be the number facts, the answer is not a sentence at all — it is ten minutes a day until 7 and 8 stop needing fingers. Dull, but it is the only thing that works, and it works quickly.

Name the one thing plainly and it is worth more than a whole set of extra papers — because every future paper will keep asking the same thing, and now your child will keep getting it right.

And it is worth knowing when to bother. A mistake made once is just a mistake. The same mistake three times is a habit, and a habit is something you can actually do something about.

One honest limit to all of this

Those three are kinds of cause. They are not a list of mistakes.

Underneath them sit a great many specific ones, and children vary enormously. Two children can both be dropping marks on fractions and be doing entirely different things wrong — one is taking the fraction of the wrong amount, the other is stopping halfway through simplifying. Same topic, same score, same teacher. Different problem, and a different ten-minute fix.

This page can tell you which kind you are dealing with. It cannot tell you which mistake your child is actually making, because that depends entirely on your child.

Finding that out means going through every question they got wrong and working out what those questions have in common — not what topic they came from, but what the child had to do in each one. It is genuinely possible at a kitchen table. It takes a couple of hours, a marked paper, and a willingness to be systematic about it.

Or you can let a paper do it for you. Ours are built for exactly this: every question is written to catch one specific mistake, so the pattern in what your child got wrong is the answer, not something you have to go looking for.

---

The SillyMaths Insight

Our papers do that comparison for you. Every mistake is tested at least twice — once in an easy question and once in a hard one — and the easy questions are deliberately placed last, against the clock, when a child is most likely to rush. So if your child gets it right early and wrong at the end, they know the method and ran out of time. If they get it wrong in both places, they have learnt something incorrectly. And because the answer booklet names the mistake behind every question, a run of wrong answers whose working was sound points at the number facts rather than the reasoning. One paper, all three readings — and you don't have to work any of it out yourself.

[Try the free demo paper →]

Twelve questions. The answer sheet names the exact mistake behind every wrong answer — and tells you whether your child knew it and rushed, or never knew it.

---