This thesis re-examines possible links between literacy and cognitive development from a medium perspective, where the child\u27s engagement in literacy is assumed to enable literacy-specific forms of thought, and where the explanation for the nature of those cognitive forms is to be sought in the examination of how the physical and semiotic properties of literacy modify the child\u27s symbolic interactions and thought. Specifically, I argue that the existing research suggests that at the onset of literacy the child acquires the ability for metalinguistic awareness. This can be explained by the fact that writing codifies speaking, thus turning words into objects of conscious reflection. I propose a reinterpretation of Piaget\u27s stage of concrete operations within the literacy framework. Further, I argue that metalinguistic awareness enables the emergence of verbal thought, which, after a period of differentiation from the concrete context, can function independently from concrete, perceptual reality. This, I suggest, leads to the achievement of what I call decontextualized thought, which I argue lies at the origins of Piaget\u27s formal operations. I outline several explanations for the emergence of decontextualized thought, and argue that the structural explanation, that writing codifies speaking and that phonetic writing characters are arbitrary with regards to the concrete image, is most central for the understanding of literacy effects. This thesis provides a critical overview of selected central contributors to the literacy hypothesis, addresses several most pressing controversies, and sketches a broader theoretical framework that places the literacy hypothesis within a constructivist framework that stresses the role of child\u27s activity. I suggest that literacy should be treated as an enabling and necessary but not sufficient factor for the emergence of literacy-specific cognitive forms, and that most past criticism of the literacy theory applies only to the \u27strong\u27 view of literacy as a sufficient cause. Because of the scarcity of direct research on literacy guided by the medium approach, much of the empirical research that I review requires reinterpretation. Hence, the current thesis is largely a hypothetical proposal of theoretical and empirical directions that the literacy hypothesis might take
