The front leaves it alone, the end may not
The Short Answer
A prefix is added to the front of a word and the root does not change, so possible stays possible inside impossible. A suffix is added to the end, and sometimes the root changes and sometimes it does not: happy becomes happiness, but kind simply becomes kindness. Knowing which endings change is most of what spelling questions of this kind ask. The complication is that a prefix sometimes changes its own shape to suit the word it joins.
What are prefix and suffix questions?
Your child is asked to add something to the front or the end of a word, or to identify what has been added, or to spell the result.
The whole family rests on one difference, and it is worth saying out loud at home: the front leaves it alone; the end may not.
A prefix does not touch the root
Add un- to necessary and you get unnecessary — with two n's, because necessary keeps every letter it started with and the prefix simply arrives in front of it.
Children write unecessary because two n's look wrong. They are trusting the eye over the rule, and the eye is not reliable on a word this shape.
The same thing happens in unnatural, unnamed, misspell, dissatisfied. Nothing is merged and nothing is dropped. That holds for the prefixes your child will be asked to add at this level — un-, dis-, mis-, in-, re-, pre- and the like — which is all the rule needs to cover.
A suffix sometimes does
Often nothing happens at all. Kind becomes kindness, help becomes helpful, quick becomes quickly, play becomes playing. The root is exactly as it was.
And sometimes the root changes. Add -ness to happy and the y becomes an i: happiness. Add -ing to hope and the e drops: hoping. Add -ing to run and the n doubles: running. Add -ing to travel and, in British English, the l doubles: travelling. Add -able to notice and, unusually, the e stays — noticeable — because it is doing a job, keeping the c soft.
So a suffix question is a question about whether the root changes, and a prefix question is a question about a root that does not.
The diagram puts one of each side by side, using the same suffix both times.
The prefix that changes shape
One complication, and it is the one that catches children who have understood everything else.
In- becomes im- before a p or a b: impossible, imbalance. It becomes il- before an l: illegal. It becomes ir- before an r: irregular.
The prefix adapts to the word it joins. The word it joins does not adapt at all. That is the point to keep hold of, because a child who notices the prefix changing may conclude that anything can change, which is exactly the wrong lesson.
Can you show me a worked example?
Where do pupils lose marks?
Dropping a letter from the root after a prefix — unecessary, misspel.
Failing to change the root when the suffix calls for it — happyness, traveling in a British English paper. And the reverse: changing a root that should have been left alone.
Assuming the prefix change means the root changes too. It does not.
Try it yourself
Say whether you are adding to the front or the end before you spell anything.
- Add un- to necessary.
- Add in- to possible.
- Add -ness to happy.
- Add -ing to travel.
- Add -able to notice.
- unnecessary. A prefix, so necessary keeps every letter — which is why there are two n's. Children who write unecessary have quietly changed the root, which adding a prefix does not do.
- impossible. Also a prefix, and here the prefix itself changes shape: in- becomes im- before a p. The root is untouched, which is the part that matters.
- happiness. A suffix, and here the root changes — the y becomes an i, as it does when a word ends in a consonant followed by y. Compare kindness, where nothing changes at all.
- travelling. A suffix, and in British English the l doubles. American English does not double it, which is worth knowing if your child reads a lot of American books.
- noticeable. A suffix, and this one keeps the e that would usually be dropped, because the e is what keeps the c sounding soft. Drop it and you get notic-able, which would be read with a hard c.
How much practice does this type need at home?
Build rather than spell. Give your child a root word and ask what can go on the front, what can go on the end, and what each addition does to the meaning.
Help gives helpful, helpless, unhelpful, helper. Four additions, four different jobs, and a root that does not change in any of them. Then try happy: unhappy leaves it alone, while happily and happiness both turn the y into an i. Ten minutes of that teaches more than a spelling list, because it teaches the machinery — and the machinery works on words your child has not met yet.
Free: an English workbook
Questions across the English 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
What is the one rule to hold on to?
The front leaves it alone; the end may not. Adding a prefix such as un-, dis-, mis-, in- or re- does not change the spelling of the root word, so if your child has added something to the front and a letter has gone missing from the original, they have made an error. A suffix sometimes changes the root and sometimes leaves it exactly as it was: quick becomes quickly with nothing altered, while happy becomes happiness. So after adding to the end, check the last letters of the root — a consonant followed by y, a silent e, or a short vowel followed by one consonant are the three signs that something may need to change.
Why does unnecessary have two n's?
Because un- ends in n and necessary begins with n, and the prefix leaves the root alone. Nothing is merged or dropped. The same thing happens in unnatural and unnamed. Children write one n because it looks odd with two, which is a good example of why the rule has to be trusted over the eye.
Why does the prefix sometimes change?
For ease of saying. In- becomes im- before p and b — impossible, imbalance — and il- before l, as in illegal. The prefix adapts to the word that follows it, but it still does not alter that word. So the root is the fixed point in both cases, which is the thing to hold on to.
How do we practise this?
Build words rather than spell them. Give your child a root — help, possible, happy — and ask what can go on the front and what can go on the end, and what each addition does to the meaning. That is more useful than a spelling list, because it teaches the machinery rather than the individual words, and the machinery works on words they have never met.
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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