CLIL stands for Content and Language Integrated Learning and describes a dual-focused form of teaching a subject: through a foreign language by being at the same time exposed to learning of content and learning of a foreign language. Since English is a global language this modern instructional foreign language education provides authentic settings by creating real-world situations. In this work the challenges of Differentiation in a Primary CLIL classroom will be examined theoretically as well as analysed according to experiences of teachers of CLIL classes gained through an interview. The work poses the question how teachers can effectively plan for CLIL and what competences teachers need to successfully hold a CLIL lesson.