This study is part of a broader interdisciplinary research project on Content and Language Integrated Learning (CLIL) in French-speaking Belgium (Hiligsmann et al. 2017). In this talk, we will present the different aspects of the project and then focus as a case study on the acquisition of intensifying constructions within this context. Intensification can be expressed cross-linguistically by several morphological and syntactic constructions (among others, Kirschbaum 2002; Hoeksema 2012; Zeschel 2012; Rainer 2015). The diversity of constructions and the language-specific preferences for particular types of intensification may complicate the acquisition of intensifying constructions for second language learners. Our research is situated within the theoretical framework of usage-based Construction Grammar and Construction Morphology (cf. Tomasello 2003; Booij 2010; Goldberg 2010 among others). Second language acquisition is presumed to be complex because of the competition between L1 and L2 constructions (Ellis & Cadierno 2009). This study focuses on one specific case of such constructional competition, namely the expression of adjectival intensification in the interlanguage of French-speaking learners of Dutch or English. More specifically, we will address three research questions: (i) Do French-speaking pupils encounter difficulties when they acquire English or Dutch intensifying constructions, and to what extent are these problems due to cross-linguistic differences? (ii) Does more input provided through a CLIL approach lead to a more native-like acquisition of intensifying constructions? (iii) What developments can we observe in the learners’ use of intensifying constructions from a longitudinal point of view (over the course of two school years)? The data for this study come from a corpus of the written productions in the form of fictional e-mails on the subject of a party or holidays. We compare texts written in 2015 and in 2017 by the same French-speaking secondary school pupils (aged 16-18), in CLIL ...