Inclusive education came into the spot light with the World Conference on Special Needs Education: Access and Quality, held in Salamanca, Spain in June 1994. The problem investigated in this study is how teaching oral hearing impaired learners in an inclusive school affects the classroom practice of the mathematics teacher as teaching-and-learning expert. In this study, the term hearing impaired refers to learners with a bilateral, moderate to profound hearing loss who have hearing aids and/or cochlear implants. These learners communicate orally, in other words, they have developed spoken language and do not communicate using sign language. The study focused on the classroom practice of three teachers in three different phases, namely the Intermediate Phase (Grade 4-6), the Secondary Phase (Grade 7-9) and the Further Education and Training phase (Grade 10-12) and explored how they teach mathematics to Hearing Impaired (HI) learners in an inclusive school. A qualitative research approach was followed and the research design was an exploratory case study. The data was collected in an inclusive school that includes oral HI learners which was purposefully chosen due to its model of inclusion where oral HI learners attend the same classes and lessons as their hearing peers. Three data collection instruments were used, namely semi-structured interviews, lesson observations and documentation analysis. The data was analysed deductively according to the themes reflected in the conceptual framework. The conceptual framework was based on ten practices mathematics teachers should apply when teaching HI learners (Easterbrooks & Stephenson, 2006), but through the lens of the mathematics teacher as teaching-and-learning expert and the language factors in teaching mathematics to HI learners. The research revealed that not all teachers who teach at an inclusive school truly understand the concept of inclusion and that continuous training is a pre-requisite for inclusion to be successful.