The aim of this paper is to show that learning to speak and write is based on cognitive foundations, apart from the social and neurological aspects which should not be underestimated. The paper should thus be read from the perspective of genetic psycholinguistics, which places special emphasis on the cognitive development that underpins oral and written language. I intend to highlight the conditions that are required for successful entry into writing, ranging from mastery of the notions of number and class and their relationships of equivalence and inclusion, to the ability for cognitive decentralisation that accompanies abstraction, which is indispensable to the symbolisation that is at the origin of the phonographic code. This paper consists of two parts: the first is focused on theoretical notions without which it would be difficult to understand the perspective adopted, and the second is more practical, documented by a battery of tests that aim to evaluate the child upon entry into school, considering the aspects listed.