This article presents the findings of an action research project conducted with a group of pre-service teachers of a program in modern languages at a Colombian university. The study intended to go beyond an emphasis on linguistic and textual features in English as a foreign language argumentative essays by using a set of genre-based activities and the understanding of writing as a situated social practice. Data were gathered through questionnaires, semi-structured interviews, class recordings, and students' artifacts. The results showed that genre-based activities supported the participants throughout the experience and boosted their confidence, resulting in a positive attitude towards essay writing. The study highlights the importance of dialogic interaction to provide scaffolding opportunities, of understanding writing as a process, and of the use of samples and explicit instruction to facilitate writing.