This research aims to analyse a teacher's questioning activity using oral open-ended questions in the mathematics classroom in three phases: the teacher asks open-ended mathematics questions orally, students answer the questions, and the teacher responds to the answers. This research involved a mathematics teacher and twenty-three year 7 students (aged eleven-twelve years old) in a secondary school in the UK. The samples were chosen using purposive sampling technique. The data collection technique used was three 45-minute-long lesson observations using field notes and audio-recordings. The notes and the transcript of the recording were analysed to find the answers for three research questions. The results showed that the teacher posed any kind of questions orally. The teacher asked two or three oral open-ended questions. Students answered those questions with different answer. The answers were not only correct, but also incorrect and incomplete. After getting an answer, the teacher responded by asking follow-up questions both closed and open-ended.