This paper reports the results of a case study with three embedded units on the impact of a genre-based EFL pedagogical intervention on students’ written narratives. The participants included three Spanish-speaking EFL students enrolled in a B1 general English course at a private language centre in Bogota, Colombia. In order to assess impact, a triangulation of qualitative and quantitative data was carried out. Data collection instruments included analyses of students’ writing samples before and after the intervention, a teachers’ questionnaire, and semi- structured interviews with students. The findings suggest that the genre-based intervention had a positive impact on the schematic structure of EFL students’ written narratives, and the nature of this impact was related to specific aspects such as genre organisation, development of ideas in paragraphs, and use of linking devices, although this impact was less marked for a student who had already shown awareness of the basic schematic structure of a narrative before the intervention.