What Is MLU and Why Does It Matter for Kids with Language Delays?

As a Speech-Language Pathologist, I often talk to families about something called MLU, or Mean Length of Utterance. Simply put, MLU refers to the average number of words or morphemes (the smallest units of meaning, like “-ing” or “s”) a child uses per sentence. It gives us a helpful snapshot of a child’s language development. Children with language delays often have a low MLU for their age, meaning their sentences are shorter and simpler than expected for their age compared to the average. Understanding MLU helps parents and therapists track progress and decide what kinds of language strategies will be most useful.

How Low MLU Might Show Up at Home

When a child has a low MLU, you might hear a lot of single-word responses like “ball” or “milk” instead of more complex phrases like “I want ball” or “more milk please.” They may rely heavily on gestures, have trouble combining words, or use memorized phrases without adding new words. This can make it difficult for them to express their thoughts or needs clearly—and for parents, that can be frustrating and worrisome. But there’s a lot you can do to support your child’s language growth right at home.

Tip #1: Use "Expansions" to Add One Word

A simple and effective strategy is to expand what your child says by adding just one word. If your child says “car,” you can respond with “big car” or “red car.” If they say “go,” you can model “go fast.” The goal is to gently stretch their language without overwhelming them. You’re not correcting—they’re not wrong—you’re just offering the next level up. This method gives your child examples of how to combine words and gradually increases their MLU.

Tip #2: Turn Repetitive Play Into Language Practice

Many children with low MLU enjoy repetitive play—pushing the same toy truck or feeding a doll the same way every time. Use this to your advantage by adding consistent phrases to those routines. For example, during car play, say “Ready, set, go!” or “Push the truck.” Repetition helps reinforce these phrases. As your child becomes familiar with them, pause at the last word and let them fill in the blank. For instance, say “Ready, set…” and wait to see if they say “go.” This builds confidence and encourages word combinations.

Tip #3: Use Choices to Encourage Word Use

Another great strategy is offering forced choices. Instead of asking open-ended questions like “What do you want?” ask, “Do you want apple or banana?” As your child gets more comfortable, model full sentences like “I want banana,” and wait to see if they’ll imitate. The key is modeling language at one step above what they’re currently using. If they usually use two-word phrases, model three-word sentences. It’s a simple way to scaffold their learning and increase their utterance length naturally.

Tip #4: Make Room for Responses—Don’t Fill the Silence

It’s easy to jump in and fill the silence when your child doesn’t respond right away, but try to pause and give them time. After you ask a question or model a sentence, count to five silently in your head. Children with language delays often need more time to process and respond. That extra pause can make the difference between a missed opportunity and a new word combination. And when they do respond, celebrate it—even if it’s just a small attempt.

Tracking and supporting MLU doesn’t mean drilling your child or turning everything into a lesson. It’s about weaving language opportunities into everyday moments—meals, play, routines—and meeting your child where they’re at. If you’re unsure what’s typical for your child’s age or want a plan tailored to their needs, a speech-language pathologist can help assess their MLU and guide next steps with personalized language strategies. Language growth doesn’t happen overnight, but with the right tools and encouragement, it can happen in the most meaningful ways.