The present study examined the use of narrative categories and mental state words in the fictional, personal, and hypothetical stories written by 150 children in the third, fourth, and fifth grades of primary school. There were three main results. First, children were better able to write fictional and hypothetical than personal stories, when considering the total number of narrative categories and the percentages of stories including at least one complete episode. Second, there was clear evidence of differentiation between the three tasks, both in terms of narrative categories and mental state language. Third, the use of mental state words correlated with the frequency of subordinate propositions and the number of narrative categories included in the stories. These findings support the hypothesis of a bidirectional interaction between lexical and syntactic development and suggest that narrative writing involves metalinguistic abilities directly related to the spontaneous use of psychological lexicon. Educational implications are discussed.