Sounding out and blending are two different skills. Sounding out is recognising a spelling and saying its sound. Blending is holding those sounds in your head and pushing them together into a word: /s/ /i/ /t/ becomes sit.
Blending is the harder of the two, and it happens in working memory, which is small and fleeting. A child whose recall of the spellings is slow has no capacity left over to hold the sounds. That is the root of most blending difficulty, and it is why nearly every fix below is really about reducing memory load.
Test the oral blending first
Before you open a book, say a word in sounds at the kitchen table.
"Can you pass me the /c/ /u/ /p/?"
They hand you the cup. Oral blending works. The difficulty is getting from print to sound, so use the techniques below.
They look blank. Blending itself is the thing to practise, and letters can get in the way for now. Play sound-talk games with no book until it clicks.
Thirty seconds, and it tells you which of two different problems you have. The DfE Reading Framework treats oral blending as a foundation for reading words in print, so it is worth checking before anything else.
Six things to check
1. Letter names. Check this first, because it stops blending dead. A child reading mat as "em, ay, tee" is pushing together three letter names, and no amount of effort will produce a word. For reading, m says /m/. Names are useful later.
2. Too much schwa. If sit comes out as "suh-ih-tuh", your child is blending six sounds instead of three. Stretchy sounds like /s/, /m/, /f/ and /l/ can be held cleanly with no schwa at all, so use them. Stops like /t/, /p/, /b/, /d/, /g/ and /k/ cannot be made entirely alone, because a little vowel always escapes. Keep it short and quiet. Do not worry that you cannot remove it.
3. Gaps that are too long. By the time they reach /t/, the /s/ has gone. Say the sounds faster and closer, then closer still.
4. Spellings that are not automatic. If your child has to stop and think what m says, working memory is full. Go back to spelling recognition for a week.
5. Words that are too long. Blending three sounds is one job. Five is another. Start at three.
6. Adjacent consonants. Just as three-sound words get easy, along come stop, plan and flag. Children who were flying can stall. Normal, not a regression.
Successive blending
If your child blends orally but falls apart with three sounds on the page, build the word as you go.
Take sat. Say /s/ /a/ and blend just those two: "sa". Now add /t/: "sat".
Two items in working memory at a time instead of three. For a child who loses the first sound before reaching the last, this is usually what works, and it is what specialist teachers reach for first. It works on adjacent consonants too: /s/ /t/ becomes "st", then add /o/, then /p/.
Keep a finger moving under the word as you go, left to right, one pass.
Practise it backwards and sideways
Blending and segmenting are the same operation in opposite directions. Alongside reading sat, ask your child to build it with magnetic letters. Children who cannot read a word can often spell it, and spelling shows them the word is made of parts.
Then manipulate. Change one sound and see what happens. Swap the /a/ in sat for /i/ and you have sit. Change the /t/ to /m/ and you have Sam. This costs nothing, needs no materials, and does more than almost anything to show a child that words are movable pieces, not memorised shapes.
What to do tonight
Model it first. Say "/s/ /a/ ... sa ... /t/ ... sat" yourself, several times, and let them join in at the end.
Start with stretchy first sounds. Sam, mat, sit and fit are far kinder than cat or pot.
Play sound-talk in the car, in the bath, on the school run. Same skill, no book, no pressure.
Stop after five minutes. Blending is tiring. Five focused minutes beat twenty miserable ones.
When to raise it with school
Sooner than you think. If your child is practising regularly, is secure on the spellings, and blending still is not happening, say so. No need to wait a term. Teachers would far rather hear early.
Raise it sooner still if reading difficulties or dyslexia run in the family. Difficulty holding sounds in working memory is one of the things specialists look at, and family history is a recognised reason to look early. The British Dyslexia Association has guidance on the signs.
Older readers
All of the above applies at nine as much as at five. The technique does not change. The books do.
An older child working on blending needs decodable text with characters and stories that suit their age, not a book about a duckling. Handing a ten-year-old an infant reader teaches them something about themselves you would rather they did not learn.
Which books help
Short words, spellings your child already knows, stretchy sounds at the front.
Book one of Tip Top Phonics uses only s, a, t, i and m. Its reading list is Mim, Sam, sit, mat, Tam. Three sounds each, most starting with a sound you can hold. What does not help is a book with words your child cannot decode, because every unreachable word is an invitation to guess.
One last thing
For some children, blending arrives in a few weeks and looks sudden. For others, it takes months of short, regular practice with no single moment where it clicks. Both are normal, and the second is more common than the first.
None of this is a reflection of anything you have or have not done. Blending is a developmental step and it comes when it comes. Short practice helps. Worry does not, and children read it off you from across the room.
Sources
Department for Education (2023) The Reading Framework. gov.uk
British Dyslexia Association, guidance on signs of dyslexia. bdadyslexia.org.uk