Pupils are currently said to have difficulties in learning as soon as they make spelling mistakes. Enlightened by recent research on the acquisition of the French written language system inspired by constructivist and interactionist models, this article aims to question such a point of view. Young writers' metalinguistic explanations show that mistakes depend on their actual (and evolutive) understanding of a complex linguistic functioning. In other respects, an approach based on verbalisation and confrontation appear to be decisive in leading children towards morphosyntactic instead of mophosemantic processes. Therefore, a diagnosis of learning difficulties should not be made too soon, and not before a specific study of wrong representations has been undertaken.