The term intelligibility refers to clarity of speech or the amount of a speaker's expressions that a listener can easily understand.

Age and Intelligibility:

By 18 months, a child's speech is typically 25% intelligible to unfamiliar listeners

By 24 months a child's speech is typically 50-75% intelligible to unfamiliar listeners

By 36 months a child's speech is typically 75-100% intelligible to unfamiliar listeners

(Source: Lynch, Brookshire, & Fox, 1980, p. 102, cited in Bowen, 1998). 

Speech Sound Development Norms:

A child’s speech is considered delayed, and speech therapy would be recommended, if they are unable to correctly produce:

H, W, M, N, P, B, and D by the 3rd birthday

Y, NG, T, K, G, and F by the 4th birthday

V, S, Z, L, SH, and CH by the 5th birthday

J, R, and THE by the 6th birthday

TH by the 7th birthday

(Source: Crow & McLeod, 2020, p.1-15).

Articulation Goal Examples:

Pronunciation of speech sounds that are currently in error; for example:

Substituting a T sound for the K sound (e.g., car = “tar”; back = “bat”)

Substituting a W sound for the L sound (e.g., lizard = “wizard”)

Distorting a S sound due to tongue touching teeth or between teeth (lisp)

Sequencing of sounds into words or sequencing of words into sentences

Overall speech clarity