Citing this article
This page contains an article about preschoolers' speech intelligibility. Cite it as:
Bowen, C. (2006). Speech Intelligibility from 12 to 48 months. Retrieved from www.speech-language-therapy.com/intelligibility.htm on (date).

Intelligibility
The term intelligibility refers to the proportion of a speaker's output that a listener can readily understand. In typical development, as children learn to talk, their comprehensibility to those around them steadily increases.

In young children there is often quite a marked difference between single word (SW) and conversational speech (CS) intelligibility; between intelligibility to their close family members and intelligibility to unfamiliar listeners; and intelligibility in known versus unknown conversational topics. With regard to families, siblings may sometimes be more adept than parents in comprehending what their little brothers and sisters are saying.

A key characteristic of children with speech sound disorders is that they are often significantly less intelligible than non-speech-impaired children of the same age.

An early source of typical intelligibility criteria came from Weiss (1982) who suggested that a child's speech should be:

26-50% intelligible by 2;0
51-70% intelligible by 2;6
71-80% intelligible by 3;0

Intelligibility to parents: 18-36 months
Table 1 provides a rough guide to how clearly a child should be speaking in the age-range 18 to 36 months. It is important to bear in mind that there is considerable individual variation between children. If, as a parent, you are in doubt about your own child's speech sound development or speech clarity, an assessment by a speech-language pathologist will quickly tell you if your child is 'on track' and making the right combination of correct sounds and 'errors' for their age.

Intelligibility to strangers 12-48 months
A handy formula suggested by Dr Peter Flipsen Jr (here; see also Flipsen, 2006) and others is used by some SLPs as a guide to the expected conversational intelligibility levels of preschoolers talking to unfamiliar listeners, or "strangers". The formula fits well with the suggestions of Coplan & Gleason (1988) and is:

AGE IN YEARS / 4 x 100 = % UNDERSTOOD BY STRANGERS:

Child aged 1;0 = 1/4 or 25% intelligible to strangers
Child aged 2;0 = 2/4 or 50% intelligible to strangers
Child aged 3;0 = 3/4 or 75% intelligible to strangers
Child aged 4;0 = 4/4 or 100% intelligible to strangers

Pascoe (2005) is in general agreement, and says, "By three years of age, a child's spontaneous speech should be at least 50% intelligible to unfamiliar adults"... "By four years of age, a child's spontaneous speech should be intelligible to unfamiliar adults, even though some articulation and phonological differences are likely to be present."

Intelligibility in general 24-48 months
Alternative, usually unreferenced, guidelines are available on the Internet. For example these Speech Intelligibility Guidelines come from HelpForKidSpeech.org.

By 2;0 a child's speech should be 70% intelligible (to ?)
By 3;0 a child's speech should be 80% intelligible
By 4;0 a child's speech should be 90% intelligible

Like the Weiss (1982) scale, this particular scale does not indicate whether the percentages relate to conversational or single word intelligibility, nor whether they refer to familiar or unfamiliar listeners.

Less than 66% percent
In Dr Michelle Pascoe's helpful Speech Intelligibility article on the Apraxia-Kids web site she cites Gordon-Brannan & Hodson (2000) who determined that children above the age of 4;0 with speech intelligibility score of less than 66% should be considered as candidates for Speech-Language Pathology intervention. What this means is that if less than 2/3 of the utterances of a child aged 4;0 in conversation with an unfamiliar listener can be understood by that listener, then intervention is indicated. Unfamiliar listeners should be able to understand at least 66% of what a child of 4;0 says.

Intelligibility Rating Scale
In the Quick Screener child speech assessment procedure described here a simple, subjective 5-point conversational speech intelligibility rating scale is used. It is useful to have an intelligibility rating from a child's parent or parents, SLP and a "stranger" (unfamiliar listener). The scale is:

1: completely intelligible in conversation
2: mostly intelligible in conversation
3: somewhat intelligible in conversation
4: mostly unintelligible in conversation
5: completely unintelligible in conversation

References
Bowen, C. (1998). Developmental phonological disorders: A practical guide for families and teachers. Melbourne: The Australian Council for Educational Research Ltd. details here

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

Flipsen, P., Jr. (2006). Measuring the intelligibility of conversational speech in children. Clinical Linguistics and Phonetics. 20, 4, 202-312. ABSTRACT

Gordon-Brannan, M., & Hodson, B. (2000). Intelligibility/Severity Measurements of Prekindergarten Children's Speech. American Journal of Speech-Language Pathology, 9, 141-150. ABSTRACT

Lynch, J.I., Brookshire, B.L., & Fox, D.R. (1980). A Parent - Child Cleft Palate Curriculum: Developing Speech and Language. CC Publications, Oregon.

Pascoe, M. (2005 May). What is intelligibility? How do SLP's evaluate and address children's intelligibility intervention? The Apraxia-Kids Monthly, 6, 5. http://www.apraxia-kids.org/site/c.chKMI0PIIsE/b.980831/apps/s/content.asp?ct=911039  Accessed August, 2005.

Schiavetti, N. (1992). Scaling procedures for the measurement of speech intelligibility. In Kent, R. D. (Ed.), Intelligibility in speech disorders.(pp. 11-34). Philadelphia, PA: John Benjamins.

Weiss, CE (1982). Weiss Intelligibility Test. Tigard, OR: CC. Publications.

Table 2: Phonological Processes

Table 4: Phonetic Development

Q&A: Speech Sound Disorders

Developmental Phonological Disorders

Typical Speech Acquisition

Typical Language Development

Page updated 04 Feb 2010

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