In Europe, bilingual subject-matter teaching - defined as "any dual-focused educational context in which an additional language, thus not usually the first language of the learners involved, is used as a medium in the teaching and learning of non-language content” (CLIL Compendium, 2009) - is booming even if the consensus about the real meaning of buzz-words, ranging from "total immersion" to "CLIL", seems to be somewhat shady. Likewise, the methodology of the learning / teaching arrangements can hardly be said to be based on a common theoretical concept (Zydatiss, 2007; Wildhage & Otten, 2003). In spite of such shortcomings, a whole range of studies (wbz, 2009; Bürgi, 2008; Hollenweger et al. 2005; Finkbeiner, 2003) have claimed the benefits of bilingual subject-matter teaching for quite a number of years. Apart from clearly heightened foreign language performance due to meaningful contents these seem to be the students' heightened motivation, their more elaborate cross-cultural sensitivity, a clearer link between instructed language teaching and its everyday, out-of-school use, the enhancement of autonomous learning and a goal-oriented development of concepts, understanding and utterance, henceforth also an improvement of the students' self-concepts and their notions of learning.The 2009 research project focused on the bilingual classrooms of a Swiss high school. The goal of the study was to show the kind of impact of bilingual subject-matter teaching on the students' language performance, on their attitude towards learning, and on their self-concepts as language learners and as students in the three bilingually taught subjects geography, biology, and chemistry. As the research project included three test intervals it was furthermore intended to examine possible changes of this impact after a didactic intervention (concept maps) in each of the three subjects.

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