The key mistakes that cost the most marks in the 11+

Most children who miss out on a selective place do not fail because the questions were too hard. They fail because they have not practised enough, or because they lost marks on questions they could do by making mistakes.

That distinction matters, because the problems have completely different fixes. A child who cannot do simultaneous equations needs teaching. A child who can do them but keeps handing in the wrong answer needs something else entirely.

Having written several thousand practice questions across the four GL papers, and having had to design the wrong answers as carefully as the right ones, I have ended up with a detailed picture of how marks actually get lost. The same patterns come round again and again.

1. Answering the Question Next to the One That Was Asked

A question asks how much bigger the largest angle is than the smallest. The child finds the smallest angle - correctly - and writes that. A question about a square asks for the distance round the outside; the child calculates the area.

In every case the mathematics was right. The reading was wrong.

What helps: get your child into the habit of underlining what the question actually wants before starting, and checking the final line against it before moving on. It sounds trivial. It is worth more marks than any topic they could revise.

2. Taking the Fraction or the Percentage of the Wrong Thing

Fraction questions in the 11+ are rarely testing whether a child can find three-quarters of something. They are testing whether the child noticed three-quarters of what.

A tank is three-quarters full. Two-thirds of the water is used. A great many children take two-thirds away from three-quarters, which treats the two-thirds as a fraction of the tank. It is two-thirds of the water that is in the tank, which is a different sum and a different answer.

The same trap runs through the money and measures questions. A bag of rice with the lowest price on the label is not the best value if it is also the smallest bag - the comparison has to be per hundred grams, not per bag.

What helps: make your child say the whole out loud. "Two-thirds of what?" If they cannot finish the sentence, they are not ready to start calculating.

3. Assuming Things Combine When They Do Not

Some quantities add up, whereas others do not. The 11+ leans on this hard.

Six children average 24 marks. Two more join, and all eight now average 26. The tempting answer for what the two newcomers averaged is 25, halfway between the two figures. It is 32, because six children and eight children do not carry equal weight, and the only safe route is to turn each average back into a total.

A price is cut by twenty per cent, then by a further ten per cent. That is not thirty per cent off the original price, because the second reduction applies to the already-reduced price.

What helps: teach the rule that averages and percentages must be converted into totals before anything is added or subtracted. It is one habit and it covers a large family of questions.

4. Counting the Ends

A surprising number of marks turn on whether the endpoints are included.

How many numbers lie between 820 and 1520? The answer depends entirely on whether "between" includes both ends, one end, or neither - and the question will have been written to make that ambiguity the whole point. The same thing happens with fence posts and gaps, with dates, and with anything arranged in a line.

What helps: for any counting question, sketch the first three and the last three items rather than reaching for a formula. The off-by-one becomes visible immediately.

5. Spotting One Rule and Stopping

This is the non-verbal reasoning version of the same problem, and it is the most common reason for lost marks in that paper.

A sequence changes shape, shading, and position all at once. The child spots the rotation, finds an option that rotates correctly, and selects it - without checking that the shading and the count also follow. In a well-written question, at least two of the wrong options will satisfy one part of the rule perfectly.

Non-verbal reasoning questions almost never turn on a single change. They are deliberately compound, and the distractors are built for children who stop at the first thing they notice.

What helps: before choosing, make your child state every element that is changing, then test each option against all of them. It is slower for a fortnight and faster thereafter. We teach by looking at 3D views of the actual flat questions - this helps children develop the images in their minds.

What This Means for Preparation

None of these five is a topic. You cannot revise them by working through a chapter, and a child can hold every one of them as abstract advice and still lose the marks on Saturday morning.

They are habits, and habits change through being caught in the act. Which is why, when a child gets a question wrong, the useful question is never "What is the right answer?" It is "What would you have had to believe for your answer to be right?" That tells you which of the five you are dealing with - and once you know that, you are fixing something that recurs rather than correcting one question.

For families starting Year 5 now, that is the most valuable thing you can build in the twelve months you have. The content is finite, and most children learn to work at the speed required. The marks get lost somewhere else.