If you remember the Cognitive theory as proposed by Piaget and his followers, language development occurs as part of a child's wider cognitive development. If that's the case then how does something like this occur?
Researchers at the University of London’s School of Languages have observed a four-year-old boy with autistic spectrum disorder who rarely speaks spontaneously and shows little evidence of verbal comprehension but who can read aloud precociously – a phenomenon that’s known as hyperlexia.
On psychological tests, the boy is found to have a mental age of just one and half years and yet he can correctly pronounce irregular words not normally encountered by children before the age of nine. Irregular words like ‘yacht’ don’t follow the usual letter-to-sound rules and his
correct pronunciation of them betrays a level of linguistic development far beyond that predicted by his mental age.
Even when presented with novel Greek letters, he attempts to read them as English letters and numbers. “This behaviour is possibly indicative of the type of driven, compulsive, and indiscriminate reading behaviour associated with hyperlexia”, the researchers said. Indeed, the boy’s mother recalled that her son looked through newspapers with an unusual intensity before he was even two years old.
Because the boy doesn’t communicate it is difficult to gauge his actual comprehension of the words he can read. Nonetheless it remains remarkable that his reading ability “just happened”, as his mother put it, and the researchers concluded “Existing cognitive accounts are inadequate to account for the development of literacy in this child”.
ENA1 - Child Language Acquisition