How many words should a 4-year-old know?

There is no exact number, and every figure you find is an estimate with a wide margin around it. A typical four-year-old understands a few thousand words and uses many hundreds of them in speech, but the normal spread at this age is enormous, and it follows what a child has been around far more closely than it follows anything worth measuring. What matters at four is not the size of the count but whether it is still growing.

Why is there no single number?

Words understood and words said are always different figures, and they are produced by different things: a child can follow a story about a badger without ever saying badger themselves. At four the gap is large, and the understood side, which is the side that will feed reading later, is the harder one to measure.

The counting rules change the answer too. You can count the words a child uses or the word families they belong to, so run and running may count as one word or two. Names count in some counts and not in others. Words a child understands only in one setting, like bath time, are hard to place at all. Change the rules and the total moves by hundreds.

Vocabulary is also not one thing. A four-year-old who can name every dinosaur and every part of a fire engine may have no idea what yesterday means. Children learn the words for what they are around and what they care about, so their word knowledge is lumpy, and the lumps are shaped by their week rather than by ability.

What does vocabulary growth look like at four?

Not a total, but the things a growing vocabulary can do. A four-year-old whose words are arriving as expected usually asks why and how, uses time words like yesterday and later, compares things (bigger than, the biggest), follows a spoken instruction with two or three steps in it, and tells you something that happened with a beginning and an end. The clearest single sign is a word from a book turning up somewhere else entirely, in the car or at dinner, used correctly. That is a word they own.

How does vocabulary actually grow at this age?

• Conversation that goes both ways. Words stick when a child used them to get something done: to answer, to ask, to argue a point about bedtime. A question that gets a real answer attaches a word to a need, and that is what makes it stay.
• Stories read aloud. A word met inside a story arrives with a picture, a mood and a moment attached, which is a stronger binding than a meaning on its own. This is why the fifth rereading is not wasted; the later reads are where the words get a turn.
• Books a little beyond the child's reading. Listening vocabulary runs ahead of reading vocabulary, and being read to is the one way to hand over words a child could not get off the page alone.
• The current obsession. A four-year-old learning the parts of a fire engine, the names of ten dinosaurs or the rules of a card game is adding words fast, and often the hard ones first. Interest does most of the work.

What is worth watching instead of the count?

Growth, in ordinary conversation. Is your child still adding words? Do people outside the family understand most of what they say? Do they use language to ask, to joke, to complain? A child with a modest-sounding vocabulary who is using it well is not behind. A child who seems to have stopped adding words is worth a conversation, whatever their total happens to be.

When should you ask a professional?

Most of the time the answer is to keep talking and keep reading. But a few things are worth taking to a doctor or a speech-language pathologist rather than to a word count. At four, that includes a child who is not speaking in short sentences, who cannot follow simple spoken instructions, who is hard for unfamiliar adults to understand, or who has lost words they used to use. That is a judgment for someone qualified to make it, and it should not be made from a number.

Words a child already understands in speech are the ones a book can teach them to read, which is what the spoken definitions in a Story Beaver book are for, and picking a book for the stage they are at is the next step.

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