This article reports on the perceptions of teacher educators and pre-service teachers from a 5-year teacher education programme in English as a foreign language - TEFL- in Chile, concerning the implications of using a writing portfolio as a pedagogical strategy to support reflection in the learning process. The writing portfolio has its foundation in the genre-process approach to teaching writing in L2 English, and it is used systematically in the first and second years of the programme. Student-teachers write approximately 3 types of text each semester and each piece of writing comprises three drafts where they get feedback from both peers and teachers. Besides, this article assesses to what extent teachers' and students' perceptions of this strategy differ from each other. The sample is made up of 51 students from the second year, with a B1-B2 level according to the CEFR, who had already been using the portfolio for four semesters - and four language teachers who have expertise in L2 writing instruction and have incorporated the portfolio in their courses. Data were collected from three sources: a Likert-scale questionnaire consisting of 19 statements from 5 dimensions: 5 questions for lexical knowledge and use, five for morphosyntactic knowledge and use, three for textual knowledge and composition, four questions for self-editing skills and feedback, and two for the reflection process. It was filled out by both students and teachers. Additionally, the questionnaire has an optional open question. The last source of information was the four in-depth interviews, conducted individually with the four participating teachers of the study. Quantitative data from questionnaires were analysed using the package SPSS 15.0, using descriptive and inferential statistics, in this case, the student's t-test to check whether the responses from both groups were statistically different. In terms of qualitative data, content analysis was used to examine the 49 answers given to the open questions from the questionnaire, and the 2-hour recordings from interviews with teachers. Results show that both teachers and students highly value the writing portfolio as a pedagogical strategy, with a global mean of 4.11 out of 5 for students and 4.17 for teachers in the questionnaire. There were no significant differences between groups as shown by the results of the student's t-test (f=2,887; p<0,95). Although no significant differences were established between groups, there were differences between the components of the questionnaire, being the dimension of the reflection process the one with the lowest mean score. In the qualitative analysis, students focused primarily on the short-term benefits such as developing proficiency, as seen by making fewer mistakes in their writing, and also their increase in lexical knowledge on specific thematic fields, and syntactic knowledge, such as verb tenses and the increased use of linking devices. For teachers, however, the portfolio strategy contributes to long-term goals, such as the enhancement of skills that will not only be useful for them during their training years, but also in their future professional paths as teachers, such as reflection, autonomy, and the understanding of their own learning processes.