What’s Intelligibility?

Intelligibility is a term used by a speech-language pathologist (SLP) to describe the ease with which one’s speech can be understood by the listener.  The American Speech-Language-Hearing Association (ASHA) describes intelligibility as a perceptual judgment based on a child’s spontaneous speech.  Intelligibility is often expressed as a percentage (of words understood) and calculated using a recorded speech sample.  It can also be an important factor when determining a child’s need for speech-language therapy and treatment goals.


Limited intelligibility can be very impactful for a child and her parent, caregiver, or teacher.  Trying to express an idea and not being understood can be terribly frustrating for a child and even contribute to unwanted behaviors at school and home.  Conversely, being the adult desperately trying to interpret your child’s needs, especially in moments filled with strong emotion, can be equally exasperating.  Additionally, reduced intelligibility can dampen self-confidence and negatively impact children academically and socially in peer relationships. 

Who’s Listening Matters

Interpretations of intelligibility can vary mildly to wildly.  For example, a parent who spends a lot of time with a child often learns her patterns of talking and can understand more of what the child says than the clerk at the grocery store or a new friend at the playground.  Furthermore, someone who knows the child well is more familiar with her vocabulary and topics of interest, which makes it easier to guess or anticipate what the child is trying to communicate.  In addition to differences among listeners, context, tone of voice, facial expressions, and gestures can influence how well a speaker's message is comprehended.

Best Index

There are many variables impacting intelligibility, so no valid norms currently exist.  However,  here is the best index (developed from more familiar listeners) we can use to guide our goals and expectations for overall intelligible speech in children based on their age:

  • 2 years old: 50% or half of what a child says in conversation is understandable
  • 3 years old: 75% or three quarters of what a child says in conversation is understandable 
  • 4 years old: 100% or ALL of what a child’s says in conversation is understandable

If you like, enlist the assistance of a trusted listener to help gauge your child's intelligibility.  Ask a relative or teacher how much they understand when conversing with your child.  If their percentages don’t match up with the indexes above, consult with a speech-language pathologist.  She can help uncover what factors (e.g., rate of speech, mispronunciations) may be interfering with your child’s ability to be clearly understood and determine if therapy is warranted. 


- Johanna Sims, M.S., CCC-SLP


Coplan, J., & Gleason, J.R. (1988). Unclear speech: Recognition and significance of unintelligible speech in preschool children. Pediatrics, 82, 447-452.


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