Speech Intelligibility by Age — Printable Reference
Printable reference of unfamiliar-listener speech intelligibility expectations by age, pooled from Coplan & Gleason (1988), Flipsen (2006), and Hustad et al. (2021).
Overview
"How intelligible should my child be at age three?" is the single most common question a school SLP fields at intake, and it has a surprisingly defensible answer. Coplan and Gleason (1988) established the first widely used percent-intelligibility-by-age rule; Flipsen (2006) refined it with a regression across 72 studies; and Hustad, Mahr, Natzke, and Rathouz (2021) published the most recent pooled values across cerebral palsy and typically-developing cohorts. This cheatsheet pools all three into a single printable age band reference so clinicians can triangulate rather than cite one source.
This cheatsheet is a static reference intended for clinical and educational use. Every page is rendered from a peer-reviewed source and cited below the printable sheet. Clinicians must adapt to the individual patient and to the current edition of any cited instrument manual before clinical use.
How to use this sheet
Print the sheet and keep it in the intake folder next to the parent report forms. During an intake conversation, ask the parent to rate (on a 0–100 scale) what percent of the child's connected speech an unfamiliar listener understands. Find the child's age band on the printed sheet and compare against the "typical" column. If the reported value falls at or below the −1 SD column, the child meets the intelligibility-based referral criterion and warrants a full phonological evaluation. Do not use intelligibility as a standalone eligibility criterion — always pair it with a single-word articulation probe, a connected-speech PCC, and a screen for receptive language. For follow-up visits, re-score every six months to track change; the typical-to-borderline boundary narrows sharply between ages 2;0 and 4;0 and it is easy to misread a normal rate of progress as a plateau.
“Parents underestimate intelligibility by 10–20 points at intake because they understand their own child perfectly. Always ask "what would a stranger at the grocery store understand?" — that reframing usually drops the number to the actual unfamiliar-listener value.”
Automate this workflow
Stop hand-copying the intelligibility numbers into every report
Upload the session audio and ConductSpeech extracts the metrics, formats them against the published norm band, and drops a ready-to-paste present levels paragraph next to the cheatsheet values. Built for school-based SLPs on 50-student caseloads.
Printable sheet
| Age | Typical intelligibility | −1 SD referral flag | Source |
|---|---|---|---|
| 1;0 (12 mo) | ~25% | <15% | Coplan & Gleason |
| 1;6 (18 mo) | ~33% | <20% | Coplan & Gleason |
| 2;0 | ~50% | <30% | Flipsen regression |
| 2;6 | ~65% | <45% | Flipsen regression |
| 3;0 | ~75% | <55% | Flipsen regression |
| 3;6 | ~85% | <65% | Flipsen regression |
| 4;0 | ~93% | <75% | Hustad 2021 TD cohort |
| 4;6 | ~96% | <82% | Hustad 2021 TD cohort |
| 5;0 | ~99% | <90% | Hustad 2021 TD cohort |
| 6;0 | ~100% | <95% | Hustad 2021 TD cohort |
Pooled from Coplan & Gleason 1988, Flipsen 2006 regression, and Hustad et al. 2021 longitudinal TD data. Values are unfamiliar-listener percent intelligibility in connected speech.
Common pitfalls
- Using the parent's in-home rating as the reference number. Parents routinely overestimate by 10–20 percentage points because they are familiar listeners — always re-anchor to an unfamiliar-listener frame.
- Treating the Coplan rule ("age in years × 25%") as a precise cut. It is a classroom mnemonic, not a norm — use the pooled table for any decision that feeds an IEP.
- Applying the chart to a child with cerebral palsy or a motor speech diagnosis. Hustad et al. 2021 specifically noted CP cohorts depart from TD intelligibility curves by age 2;6.
- Confusing intelligibility (percent of utterances understood) with articulation accuracy (PCC). They correlate but are not interchangeable — a child can have 80% PCC and 50% intelligibility if suprasegmentals are disrupted.
Free tools paired with this cheatsheet
Speech Intelligibility by Age Calculator
Free interactive speech intelligibility calculator for speech-language pathologists. Enter a child age and the observed unfamiliar-listener intelligibility percent from a connected-speech sample, and the tool returns the typical / borderline / refer flag against the pooled Coplan & Gleason (1988), Flipsen (2006), and Hustad et al (2021) age expectations. Built for SLP intake, well-child visits, EI eligibility, and parent counselling. Mobile-friendly, client-side, no sign-up.
Open toolPCC Calculator
Free interactive Percent Consonants Correct (PCC) calculator for speech-language pathologists. Enter the consonants attempted and produced correctly from a 50- to 100-utterance connected-speech sample and get the PCC percent plus the Shriberg & Kwiatkowski (1982) severity band (mild, mild-moderate, moderate-severe, severe). Built for SLP intake, IEP eligibility, treatment-progress tracking, and graduate phonological-assessment training. Mobile-friendly, client-side, no sign-up.
Open toolSpeech Sound Development Chart
Free interactive speech sound development chart for speech-language pathologists. Look up the age of acquisition for the 24 English consonants based on the McLeod & Crowe (2018) cross-linguistic systematic review. Filter by age band and word position (initial, medial, final), enter a child age and instantly see which sounds are age-expected versus still developing. Mobile-friendly, client-side, no sign-up.
Open toolRelated cheatsheets
English Consonant Mastery Ages — Printable Chart
Printable McLeod & Crowe (2018) English consonant mastery chart with age of customary production for all 24 consonants, sorted by place and manner.
PhonologyPhonological Processes — Ages of Suppression Cheatsheet
Printable reference of the 12 most common English phonological processes with Bowen (2015) ages of suppression, definitions, and clinical examples.
Language samplingMLU-Morpheme Norms by Age — Printable Reference
Printable one-page reference of Mean Length of Utterance in morphemes (MLU-M) expectations by chronological age, including Brown, Miller, and Rice norms.
References
- Coplan, J., & Gleason, J. R. (1988). Unclear speech: Recognition and significance of unintelligible speech in preschool children. Pediatrics, 82(3), 447–452.
- Flipsen, P. (2006). Measuring the intelligibility of conversational speech in children. Clinical Linguistics & Phonetics, 20(4), 303–312.
- Hustad, K. C., Mahr, T., Natzke, P. E., & Rathouz, P. J. (2021). Speech development between 30 and 119 months in typical children I: Intelligibility growth curves for single-word and multiword productions. Journal of Speech, Language, and Hearing Research, 64(10), 3707–3719.