Increasing Sentence Length (MLU)

What is Mean Length of Utterance (MLU)?

When we talk about increasing sentence length in children, we often use the term “mean length of utterance”. This refers to the average length of the sentences that a child typically uses. For example, when children are first learning to talk, their MLU is often 1 because they only use one word at a time: “ball?”, “mommy”, “mine”, “no”. If uses a single word like this about half of the time but puts two words together the other half of the time (like “my ball”), then we would say the MLU is 1.5.


Average MLU based on Age

Here is a chart of what a child’s MLU should be a different ages :

Age MLU (in morphemes)
12-26 mos 1.0 – 2.0
27-30 mos 2.0 – 2.5
31-34 mos 2.5 – 3.0
35-40 mos 3.0 – 3.75
41-46 mos 3.75 – 4.5
47 mos + 4.5 +

How to Increase Sentence Length

So what do you do if a child’s average sentence length (or MLU) is not where it should be? Well, there’s plenty you can do! If you are a parent of a child and you are concerned about MLU, you should of course seek out the advice of a speech-language pathologist (SLP).

In order to increase sentence length, you need to determine what is missing from the child’s speech. Here are some areas to look at when considering increasing sentence length.


Increase Vocabulary

It’s possible that the child does not have a large enough vocabulary to choose words from. If the child doesn’t have a large enough vocabulary, he may not have enough words to form longer sentences. We know from research that children don’t start combining two words together (like “my ball”) until they have at least 50 words in their vocabulary.

And even then, there must be a wide range of different types of words in their vocabulary. If the child only knows 50 nouns, he’s not going to be able to combine those in many ways that make sense. “Cookie ball” doesn’t really tell us much. Unless it was a ball made out of cookies…in which case I want one. But I digress. A child’s early vocabulary must include nouns, verbs, descriptors, possessives (like “my”), negatives (like “no”), demonstratives (like “that”), question words (like “what”), etc.

If the child you are working with has a limited vocabulary, try working on that as a means of increasing vocabulary.