The Spanish region of Madrid has carried out the authorization of pre-primary and primary schools to teach the first two years of Compulsory Secondary Education. This measure has been justified by a vague need related to childcare, prevention of youth gangs, addictions and school drop-out and failure, and reconciling family and work. For the curent school year, 52 pre-primary and primary schools have signed up for this proposal (although in the end only 49 have had sufficient demand). Through interviews with the principals of schools that will implement it next year, together with the assigned secondary schools, schools that are already running these courses, schools that have not been authorized by the administration to do so and representatives of principals of pre-primary and primary schools and secondary schools, we have tried to deepen the educational needs to which this measure may be addressed. Results show that the vague pedagogical debate is articulated in two types of tensions: the understanding of the 12-14 years stage as part of childhood or adolescence, and consequently the retention purpose of primary schools and the accompanying purpose of secondary schools, and the generalist school grammar of the former and the specialized ones of the latter. These tensions raise the question of whether we are facing a process of primarisation of Compulsory Secondary Education, and the effects this may have on its comprehensive nature.