In Flanders, as in many other European countries, a language deficiency paradigm of teaching and learning – based on monolingual ideologies – has been constructed. This contribution builds on the findings of an earlier quantitative study ‘Silencing linguistic diversity: The extent, the determinants and the consequences of monolingual ideologies amongst teachers’, presented at the ECER-conference of 2013. In this study, a strong correlation was found between teachers’ monolingual beliefs and their trust in students. The stronger teachers’ monolingual beliefs, the less trust they show in their students. No correlation was found between monolingual beliefs and teachers’ self-efficacy. The new research project aims at gaining more insight into these findings by collecting supplementary qualitative data at teacher and student level in three secondary schools. To what extent do teachers reinforce, negotiate or contest monolingual policies in education? How do teachers rationalize and legitimize their monolingual perceptions? How do students experience these monolingual policies? The newly collected qualitative data will be linked with the quantitative dataset originating from the previous research project. Triangulating the quantitative and the qualitative dataset will lead to a more in-depth understanding of the dynamic interaction between language ideologies, language policies at national and school level, and teachers’ practices.