One of the key effects of globalisation is the extraordinary increase in migratory movements. Spain, a country traditionally accustomed to emigration, has seen a considerable rise in the influx of immigrant population, with notable demographic, social and cultural transformations. Particularly, since the early 90s, schools have been experiencing increasing ethnic diversity in their student enrolments. Especially, over the last 10 years, their presence has multiplied 10-fold, reaching 9.53% of the total student body. Thus, along with linguistic difference, class, gender or ability, the most characteristic feature of Spanish schools in recent years is their multicultural nature. For these reasons, it seems reasonable to focus on how Spanish schools, and particularly teachers, perceive and manage cultural diversity. This article reports on a multiple case design study concerning the teachers' views on cultural diversity and the impact on daily practice in their classrooms. Participants included 16 teachers, with experience ranging from 2 to 20 years of teaching, from four Spanish secondary schools. Semi-structured in-depth interviews with the teachers from each school were chosen as the research method. Additionally, the principal and four immigrant student families from each school were also interviewed. Further information was obtained through a focus-group interview with the four school counsellors. Over a six-month period, all the interviews and complementary field work were carried out by a researcher in each school. While recognising the efforts to accommodate ethnic groups and immigrant populations, the results indicated that teachers perceive cultural diversity as a particular problem whose management is marginalised and excluded from the set of school activities and teaching practices. Teachers agree that the issue is one of adaptation, a problem to be solved by the students themselves with the support of school counsellors and other educational specialists. This way, neither school policies nor teaching practices assume the commitments arising from cultural diversity, so we cannot say that teachers incorporate it in their work, putting culturally relevant teaching into practice in their classrooms. While one of the benchmarks achieved in recent years is the presence of educational specialists in schools to address cultural diversity, the next step is to create the conditions to articulate a joint and collaborative effort between the teaching body and these professionals, bringing cultural diversity management closer to the classroom. Another pending challenge would be determining how we can best prepare teachers for organising and managing their culturally diverse classrooms. Teachers in these schools are doing their job without a professional knowledge base concerning multicultural education. Therefore, pre-service and in-service teacher education programmes should consider questions related to multicultural education and classroom management, which are absent or rarely taken into account in teacher training to date.