Much of second language (L2) class time, particularly in school and university classes, is devoted to the teaching of writing, and written assignments form an important component of assessed work. We assume that learners' L2 writing develops over time, in response to instruction, feedback, and practice. However, to date there has been very little research to show whether all skills involved in producing a well-structured and grammatically accurate text develop uniformly and respond equally to pedagogy. Our longitudinal study explored development in writing among a group of secondary school learners of French (n=15), in their final year of high school. Data for the study were three in-class essays written by the students at regular intervals over a period of six months. The essays were analysed for global quality as well as for grammatical accuracy and syntactic complexity using several quantitative and qualitative measures. Results showed improvements at the discourse level and in linguistic complexity, but there were no significant improvements in accuracy and certain frequent errors persisted. Results also showed that students continued to rely on prefabricated chunks learned in class, but the ability to use such chunks creatively improved over time. The research and pedagogical implications of these findings are discussed.