After the publication of the "CEFR Companion Volume" in 2018, a revision of the curriculum in force for the English subject in the Bilingual Sections in the Community of Madrid has been implemented. One of the main changes is the inclusion of the concept of linguistic mediation in the subject 'Advanced English' in the last stage of secondary education. In an attempt to understand how linguistic mediation strategies and activities are being developed in real classroom contexts, this study has focused on teachers' perceptions of linguistic mediation. A questionnaire and a focus group were used to examine teachers' understanding and awareness of linguistic mediation, as well as the type of mediation activities that are relevant for their students and the extent to which they include linguistic mediation activities and strategies in their lessons. Additionally, the study has shown some of the deficiencies that exist in the way linguistic mediation is currently being addressed in the classroom, as well as teachers' needs in order to better implement it.