The present study was designed to enhance our understanding of the changing relationship between low- and high-level writing processes in the course of development. A dual description of writing processes was undertaken, based on (i) the respective time courses of these processes, as assessed by an analysis of eye and pen movements, and (ii) the semantic-linguistic characteristics of the writers' scripts. In order to conduct a more fine-grained description of processing strategies, a “case study” approach was adopted, whereby a comprehensive range of measures was used to assess low- and high-level processes within five writers with different a-priori levels of expertise in text composition (7th-, 9th- and 12th-graders, MA student, author). The task consisted in continuing an imposed incipit, by composing a personal and imaginative text. The main results showed two developmental patterns linked to expertise: (i) a gradual acceleration in low- and high-level processing (pauses, flow), associated with (ii) changes in the way the previous text was (re)read. Compared with the other less experienced writers, the author displayed greater creativeness and far higher processing speeds, due to the proceduralization of planning which maximized parallel processing. The usefulnesss and limitations of the case study approach are discussed in the conclusion