Socio-political and demographic developments in Western Europe make diversity and multiculturalism a relevant line of research and emerging topic in education sciences. This paper discusses a case study that investigates Belgian pre-service teachers' attitudes towards ethnic diversity in their classrooms, how their teaching caters to student heterogeneity and how they develop as diversity-conscious professionals. This qualitative study draws on multiple data sources (questionnaires, interview transcripts, logs, peer feedback after lesson observations and lesson plans) from three parallel cases that involve foreign and second language teaching set in significantly different contexts, resulting in three distinct intercultural cases: adult education and immigrant education in Belgium and secondary education in Morocco. Although the participants demonstrated high diversity awareness, their shared multicultural knowledge and attitudes did not prevent them from adopting strikingly divergent approaches to address cultural diversity, ranging from deliberate avoidance during lesson planning to breaching official policy in order to address identity and interculturality. The paper concludes that ideally diversity awareness in professionals is generated in proper teaching practice, which is shown to be characterized by the challenge of transferring theoretical principles to varying classroom settings through sound lesson planning.