Age	Achievement
1 to 6 months	Coos in response to voice
6 to 9 months	Babbling
10 to 11 months	Imitation of sounds; says “mama/dada” without meaning
12 months	Says “mama/dada” with meaning; often imitates two- and three-syllable words
13 to 15 months	Vocabulary of four to seven words in addition to jargon; < 20% of speech understood by strangers
16 to 18 months	Vocabulary of 10 words; some echolalia and extensive jargon; 20% to 25% of speech understood by strangers
19 to 21 months	Vocabulary of 20 words; 50% of speech understood by strangers
22 to 24 months	Vocabulary > 50 words; two-word phrases; dropping out of jargon; 60% to 70% of speech understood by strangers
2 to 2 ½ years	Vocabulary of 400 words, including names; two- to three-word phrases; use of pronouns; diminishing echolalia; 75% of speech understood by strangers
2½ to 3 years	Use of plurals and past tense; knows age and sex; counts three objects correctly; three to five words per sentence; 80% to 90% of speech understood by strangers
3 to 4 years	Three to six words per sentence; asks questions, converses, relates experiences, tells stories; almost all speech understood by strangers
4 to 5 years	Six to eight words per sentence; names four colors; counts 10 pennies correctly