In recent years, dyslexia has become an important issue in the field of foreign language teaching and learning. In this research we will explore dyslexia in connection to teaching and learning a foreign language. More particularly, in this research, we will be probing into the teaching of German as a foreign language. The purpose of this research is to investigate the effectiveness of the application of Differential Instruction, the application of the Grammar –Translation Method, the Audio-Visual Method, the Communicative Approach to language teaching as well as the Multisensory Method to a Greek student with dyslexia. The girl is in the first year of junior high school and is being taught German as a foreign language at school. The research method, which was applied, focused on qualitative research through the use of semi - structured interviews. This research is also a case study. Action research was conducted, for the needs of this small-scale research, through ten differentiated instruction lessons which were taught to a student with dyslexia. The student and her mother were the major sources of data collection. More particularly, the semi - structured interviews were conducted before and after the implementation of differentiated instruction with the student and her mother. We initially attempted to collect information through semi-structured interviews, on the student's family profile, and after conducting the ten lessons, we tried to verify the effectiveness of the approaches and methods which were applied. The results of this research showed that the effectiveness of differentiated instruction was immense as the student’s performance improved in the foreign language.