Mirror check first: letter codes
The Short Answer
A letter code question gives a word and its code side by side, and that pair is the instruction. Work out how far each letter has moved through the alphabet, writing every jump down before deciding anything. Three rules turn up most often: a same-jump code, a pattern code where the jumps alternate or climb, and a mirror code where A pairs with Z.
What is a letter code question?
Your child is given a word and its code, side by side, and asked to code or decode something else.
That pair is the instruction. The rule wanted is the simplest one that fits every letter of it, and the job is to read the pair properly before doing anything with it.
The mistake that costs the most
Look at WAVE becoming XDWH.
W to X is one. A child who sees that and starts answering has decided the rule is plus one, and will get the second and fourth letters wrong.
Keep going. A to D is three. V to W is one. E to H is three. The rule is plus one, plus three, plus one, plus three — and it was invisible until the second jump. The third letter fits plus one as well, which is why checking only some of the letters is not enough.
Write every jump down before deciding anything. That sentence is most of this lesson.
The three rules, and how to tell them apart
| Rule | What it does | How it looks |
|---|---|---|
| Same jump | Every letter moves the same distance | +3, +3, +3, +3 |
| Pattern | The jumps alternate or climb | +1, +3, +1, +3 or +1, +2, +3, +4 |
| Mirror | A pairs with Z, B with Y | H ↔ S, A ↔ Z: same distance from opposite ends |
These are the three we meet most often. Whichever it is, it has to fit every letter in the pair.
The order to work in is fixed: mirror check first, on two pairs. Then write the jumps. Then look at the jumps for a pattern.
Mirror first, because a mirror code is the one rule that looks exactly like the others until you test it. On a single letter it can pass for a same-jump code, and by the time that is discovered a whole word has been coded wrongly.
Can you show me a worked example?
The diagram shows the same check as sums. S is the eighth letter from the end, which makes it the nineteenth from the start, and 8 + 19 = 27. In a mirror code every letter and its partner have positions that add up to 27.
Where do pupils lose marks?
Miscounting. The alphabet has no landmarks in the middle, and I to K is easy to make into I to J. Counting on fingers is entirely respectable.
Going the wrong way. A jump backwards read as a jump forwards produces a plausible-looking wrong answer.
Missing a mirror, as above.
Letting a pattern stop too early. In a four-letter example the pattern +1, +3, +1, +3 has to carry on into the fifth and sixth letters of a longer word: +1 for the fifth, +3 for the sixth. Children often stop after four letters or repeat the last jump. The pattern begins again at the first letter of each new word to be coded.
Try it yourself
Write down every jump before deciding on the rule. Check for a mirror first.
- If WAVE is written as XDWH, what is the rule?
- Using that same rule, how is STORM written?
- If a code moves every letter forward two, how is TRAIN written?
- HAND is written as SZMW. What kind of code is this?
- Plus one, plus three, plus one, plus three. W to X is one, A to D is three, V to W is one, E to H is three. Stopping after the first jump would give plus one throughout, and the second and fourth letters would be wrong.
- TWPUN. Applying plus one, plus three, plus one, plus three, plus one: S to T, T to W, O to P, R to U, M to N. The pattern starts again at the first letter of the new word and keeps repeating into the fifth letter.
- VTCKP. Each letter moves forward two, and the I to K and N to P steps are the ones children miscount because they are near the middle of the alphabet where there are no landmarks.
- A mirror code. H pairs with S, A with Z, N with M, D with W — each letter is the same distance from the opposite end of the alphabet as its partner, and that holds for all four pairs. Apply the same rule to SZMW and you get HAND back, which is a good final check.
How much practice does this type need at home?
Two or three short sessions a week. As with letter sequences, the limiting factor is usually alphabet fluency rather than understanding, so the most valuable drill is counting: four after G, five before R, the mirror of C.
The mirror is worth learning as a fact rather than worked out each time. A pairs with Z, B with Y, C with X, D with W, E with V. Five pairs learned by heart cover most of what turns up, and the rest can be counted from the ends.
Free: a Verbal Reasoning workbook
Questions across the Verbal Reasoning question types, with the method printed at the top and full answers at the back. One workbook for the whole strand, not a sheet per question type.
Frequently Asked Questions
Why does my child get the first letter right and then go wrong?
Because they worked out the first jump and started answering. In WAVE going to XDWH, the first jump is plus one, and a child who assumes that is the rule codes the whole word as plus one and gets the second and fourth letters wrong. Every jump has to be written down before anything is decided. It is one of the commonest ways marks go on this type.
What is a mirror code and how do you spot one?
In a mirror code, A pairs with Z, B with Y, C with X and so on — each letter maps to the one the same distance from the other end of the alphabet. It is the one rule that looks like the others until you test it, so we check for it first, on two pairs, and then on the rest. The check is the distance from each end: the eighth letter pairs with the eighth from the end. Applying the rule to the code should also give the original word back, which is a useful confirmation but not proof on its own.
In what order should my child work?
Mirror check first, on two pairs. Then write down every jump. Then look at the jumps for a pattern. That order matters — a mirror code can masquerade as a same-jump code on a single letter, and testing for it first costs a few seconds and prevents the wrong rule being applied to a whole word.
What if the jumps neither stay the same nor alternate?
They may be climbing: plus one, plus two, plus three, plus four. Growing patterns are less common but do appear, and they are only visible once all the jumps are on the page — which is the same reason we write them down for every other case. A child who has written four jumps can see a climb instantly; a child holding them in their head cannot.
Sources
- GL Assessment — 11+ familiarisation materials and question type descriptions Published 2025.
- Clever Clogs Academy — our own Year 4 and Year 5 lesson records, Winslow Published September 2025 to July 2026.
We are not affiliated with, endorsed by or connected to GL Assessment or Buckinghamshire Council. Test arrangements change; always check the council's own pages for the current year's dates.
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