The Moroccan Ministry of Education has recently implemented a multilingual programme, called 'language alternation' (LA). The programme aims at improving students' foreign language (FL) proficiency level and promoting plurilingualism by using French, English, and Spanish, for the teaching of math, physics and life and earth sciences at the secondary level, instead of the official language, Arabic. The study sought to understand this new tendency in Moroccan education by examining official educational documents and exploring teachers' perceptions using Grounded Theory (GT), which is a hypothesis-generating methodology. The findings showed a gap between the conceptualised language recommendations in the official documents and the implementation of these recommendations in Moroccan schools. In addition, it seems that the new enacted educational policy has brought about challenges for both students and teachers. The interviewed teachers were concerned about their students' initial FL proficiency, the negative effect of the new policy on students' content learning, the lack of trainings in the methodology of the new medium of instruction (MOI) policy and limited agency of teachers in the conceptualisation and implementation of the new policy.