This paper analyses the issue of language acquisition in a psycho- and sociolinguistic perspective, discussing its behaviourist, maturational and constructionist theories. All these approaches share the feature that, with respect to language acquisition, they take both an innate language faculty and a set of environmental effects into consideration. The various approaches mainly differ in terms of the proportions of influence they attribute to each of these components. Another shared feature is that most approaches usually restrict the issue of language acquisition to the acquisition of the spoken form of one's native language. However, evidence is accumulating that, due to environmental factors, a simultaneous acquisition of the written and spoken versions of the mother tongue cannot be excluded, either. This paper presents detailed data concerning the linguistic development, with respect to written language, of a child between the ages of 2 and 4. The phenomenon analysed here, the pre-school acquisition of the written form of a child's native language, raises not only theoretical problems but also those of a very practical nature in connection with mother tongue education.