Stage: Early I  (MLU: 1-1.5)

Age (in months): 12-22

Declarative: Agent + action; Action + object

Negative: Single word—no, all gone, gone; negative + X

Interrogative: Yes/no asked with rising intonation on a single word; what and where

Conjoining: Serial naming without and

Stage: Late I (MLU: 1.5-2.0)

Age (in months): 27-28

Declarative: Subj. + verb + obj. appears

Negative: No and not used interchangeably

Interrogative: That + X; what + noun phrase + (doing)?

Embedding: Prepositions in and on appear

Conjoining: And appears

Stage: Early II (MLU: 2.0-2.25)

Age (in months): 27-28

Declarative: Subj. + copula +compl. appears

Interrogative: Where + noun phrase + (going)?

Stage: Late II (MLU: 2.25-2.5)

Age (in months): 28-30

Declarative: Basic subject-verb-object used by most children

Negative: No, not, don't, and can't used interchangeably

Interrogative: What or where + subj. + pred. Earliest inversion appears

Embedding: Gonna, wanna, gotta, etc., appear

Stage: Early III (MLU: 2.5-2.75)

Age (in months): 31-32

Declarative: Subj. + aux. + verb + obj. appears; auxiliary verb forms can, do, have, will, and be appear

Negative: negative element placed between subject and predicate

Interrogative: with copula in What/where + copula + subj.

Conjoining: But, so, or, and if appear

Stage: Late III (MLU: 2.75-3.0)

Age (in months): 33-34

Declarative: Auxiliary verb appears with copula in subj. + aux. + copula + X

Negative: Won't appears

Interrogative: Auxiliary verbs do, can, and will begin to appear in questions; inversion of subject and auxiliary verb appears in yes/no questions

Stage: Early IV (MLU: 3.0-3.5)

Age (in months): 35-37

Negative: Negative appears with auxiliary verbs (subj. + aux. + neg. + verb)

Interrogative: Inversion of auxiliary verb and subject in wh- questions

Embedding: Object noun-phrase complements appear with verbs such as think, guess, and show; embedded wh- questions

Conjoining: Clausal conjoining with and appears (most children cannot produce this form until late stage V); because appears

Stage: Late IV  (MLU: 3.5-3.75)

Age (in months): 38-40

Declarative: Double auxiliary verbs appear in subj. + aux. + aux. + verb + X

Negative: Adds isn't, aren't, doesn't, and didn't

Interrogative: Inversion of copula and subject in yes/no questions; adds do to yes/no questions; adds when and how

Embedding: Infinitive phrases appear at the ends of sentences

Stage V  (MLU: 3.75-4.5)

Age (in months): 41-46

Declarative: Indirect object appears in subj. + aux. + verb + ind. obj. + obj.

Negative: Adds wasn't, wouldn't, couldn't, and shouldn't; negative appears with copula in subj. + copula + neg.

Interrogative: Adds modals; stabilizes inverted auxiliary; some adultlike tag questions appear

Embedding: Relative clauses appear in object position; multiple embeddings appear by late stage V; infinitive phrases with same subject as the main verb

Conjoining: Clausal conjoining with if appears; three-clause declaratives appear

Stage: Post-V  (MLU: 4.5+)

Age (in months): 47+

Negative: Adds indefinite forms nobody, no one, none, and nothing; has difficulty with double negatives

Interrogative: Questions other than one-word why questions appear; negative interrogatives beyond age 5

Embedding: Gerunds appear; relative clauses attached to the subject; embedding and conjoining appear within same sentence above an MLU of 5.0

Conjoining: Clausal conjoining with because appears with when, but, and so beyond an MLU of 5.0; embedding and conjoining appear within the same sentence above an MLU of 5.0

*Based on approximately 50% of children using a structure