The paper focuses on lesson planning in CLIL - Content and language integrated learning and its relations to a priori analysis as defined by Brousseau in his Theory of Didactical Situations. The authors focus on the specifics of planning a mathematical lesson and its activities if taught through a foreign language in contrast to traditional planning of lessons.
The authors also argue that although the act of devolution is harder to achieve if pupils cannot communicate in their mother tongue, it is feasible if precisely prepared. The theoretical explanations are illustrated by examples from a CLIL unit conducted in the 6th grade in a Prague lower secondary school.