Content and language integrated learning (CLIL) refers to teaching of non-linguistic subjects (e.g. mathematics) through an additional language (L2). When using L2 to understand and learn a non- linguistic subject, a wide range of cognitive processes are activated. In our paper we will concentrate on two items related to CLIL in mathematics education: 1. The interaction of three “languages” when teaching mathematics in L2, i.e. mother tongue (L1), L2 and the language of mathematics (L2) - advantages, disadvantages, possible obstacles related to CLIL in mathematics lessons. 2. Differences in L3 discourse when teaching mathematics in L1 and/or in L2. Concrete examples from CLIL used in secondary schools and from pre-service teacher training courses at Charles University in Prague will be used during the presentation.
