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Children extract grammatical rules from heard speech through implicit statistical learning, moving from single words to two-word combinations (around 18-24 months) to increasingly complex sentences. Early grammatical morphemes (past tense, plurals, subject-verb agreement) are mastered gradually through exposure and productive use, with overgeneralization errors ("goed," "mouses") reflecting rule abstraction.
Analyze speech transcripts from longitudinal databases (CHILDES) showing progression from single words through multi-word utterances; observe overgeneralization errors as evidence of implicit rule learning rather than imitation.
Children do not learn grammar primarily through correction; they extract rules implicitly from exposure. Overgeneralization errors (e.g., 'goed') are healthy learning and indicate rule abstraction, not mistakes to punish. Adult-like grammar takes many years to acquire fully.
You already know from your prerequisite work on language acquisition that children move through predictable milestones — babbling, first words, two-word combinations — with remarkable cross-linguistic consistency. Syntax acquisition is the story of what happens next: how children go from stringing two words together to producing grammatically complex sentences, all without formal instruction and before they can read or write. The mechanism is implicit statistical learning: the brain tracks patterns in heard speech and extracts rules without conscious awareness.
Consider how a child acquires the past tense in English. At first they produce correct past-tense forms for common verbs — "went," "came," "broke" — because they've memorized these as whole-word chunks, the same way they memorized individual nouns. But then something remarkable and seemingly backward happens: they start saying "goed," "comed," "breaked." This isn't regression — it's progress. The child has abstracted the general rule (add "-ed" for past tense) and begun applying it systematically, overriding the irregular forms they previously had memorized. These overgeneralization errors are the signature of rule abstraction. Eventually, with more exposure, the child learns to treat irregular verbs as exceptions, and the errors fade. The arc — correct, then incorrect, then correct again — is called the U-shaped developmental curve, and it appears across many grammatical forms in many languages.
The developmental sequence for syntactic structure follows a similar logic. Two-word utterances at 18–24 months are already syntactically organized — children don't randomly pair words; they combine agent + action ("daddy go") or action + object ("eat cookie"), showing sensitivity to word order and thematic roles. As vocabulary grows, children begin adding grammatical morphemes: plural -s, possessive -'s, progressive -ing, the articles "a" and "the," auxiliary verbs. These are acquired in a roughly consistent order across children learning English, suggesting the sequence reflects cognitive and linguistic complexity rather than frequency of input alone.
Crucially, correction plays almost no role in this process. Parents rarely correct children's grammar explicitly, and when they do, children often ignore it. The child who says "why you didn't come?" will typically not benefit from hearing "no, it's 'why didn't you come?'" — they'll simply repeat their own version. What drives learning is sheer quantity of well-formed input: children need to hear grammatical constructions many times before implicitly extracting the underlying pattern. This is why language-rich environments — more talking, reading aloud, varied conversation — predict better grammatical development, even controlling for intelligence and other factors.
The endpoint of this developmental process is adult-like grammar, but that endpoint is further away than it appears. Most children sound grammatically fluent by age 5 or 6, but subtle aspects of complex syntax — relative clauses, passives, certain negation structures, pragmatically appropriate use of tense — continue developing into middle childhood and beyond. Acquiring the building blocks (vocabulary and simple syntax from your prerequisites) enables this later sophistication; without a rich vocabulary and solid early constructions as scaffolding, the more complex structures have nowhere to attach.