Our paper aims to present a 5-year multidisciplinary research project on immersion education in French-speaking Belgium. Our project starts from the premise that although recently published surveys have confirmed that immersion learners outperform traditional L2 learners as far as target language test scores are concerned, it nonetheless remains largely unclear to what extent, in what respect and thanks to which (internal and external) processes and factors immersion students show increased language gains compared to traditional learners (see Dalton-Puffer 2011). Drawing on an innovative combination of different research methods and perspectives, our project tackles the interplay between linguistic, cognitive and educational aspects of immersion. This interdisciplinary approach also allows us to examine the possible cognitive (memory, attention…) and socio-affective (motivational, attitudinal…) factors that inform the potential linguistic (typological, cross-linguistic…) differences between immersion learners of Dutch and English (see for instance Bialystok and Barac 2012 and Katarzyna 2012). The project aims to gather and analyse data from French-speaking immersion and non-immersion L2 learners of both English and Dutch in the last two years of primary and secondary school education. Methodologically, it takes an innovative approach, combining corpus-based longitudinal and cross-sectional analyses, attitudinal questionnaires, classroom observations, and experimental research designs. The poster will present the chosen methodology in greater detail and provide the preliminary results from a first wave of data collection. Dalton Puffer, C. (2011), Content-and-Language Integrated Learning: From Practice to Principles? in: Annual Review of Applied Linguistics 31, 182–204. Bialystok, E. & Barac, R. (2012). Emerging bilingualism: Dissociating advantages for metalinguistic awareness and executive control. Cognition, 122, 67-73. Katarzyna P. (2012). ‘The impact of students’ attitude on CLIL: A study ...