Speech Intelligibility 
The term intelligibility refers to the proportion of a child's verbalizations that a listener can understand. The following is a guide to the expected conversational intelligibility levels of preschool aged children talking to unfamiliar listeners.
| Child aged 2 = 2/4 or 50% intelligible |
| Child aged 3= 3/4 or 75% intelligible |
| Child aged 4= 4/4 or 100% intelligible |
Coplan & Gleason (1988)
In general, unfamiliar listeners should be able to understand at least 66% of what a child of 4 years old says. (Brannan & Hodson 2000)
Sound Acquisition
Generally, children should produce the following sounds correctly by the age indicated:
3 to 5 years = m,b,n,t,p,d,w,h,g,k, and vowels
5 to 6 years = sh, ch, l, l blends
7+ years= v,j,th,s,z,r, s blends, r blends
Vocabulary and Sentences
2 years = 2 word utterances
3 years = 3-4 word utterances 400-900 word vocabulary
5 years = 5-6 word utterances 1500-2500 word vocabulary
Fluency
The normally disfluent child occasionally repeats syllables or words once or twice. Disfluencies may also include hesitancies and the use of fillers such as 'uh', 'er', 'um'.
Disfluencies occur most often between ages 1 1/2 and 5 years, and they tend to come and go.
(The Stuttering Foundation)