This study explores the influence of external examination on teaching and learning Mathematics at the secondary schools affiliated with provincial and private examination boards in Pakistan. This study was conducted in two phases by employing the explanatory sequential mixed-method. First, the Mathematics examination papers of the last five years from both provincial and private examination boards were reviewed and analyzed to understand (1) the cognitive complexities required to solve the questions, (2) the frequency and variety in which the questions were repeated, and (3) the chapters of prescribed books whereby the questions were selected in the examination of last five years. In the second phase, semi-structured interviews, with teachers and students were conducted, along with participatory observation to understand how the examination patterns shape their teaching and learning. The findings revealed that the external examination directly influences teachers' teaching, and indirectly students' learning. Both the positive and negative effects of the external examination were found on the teaching-learning strategies of teachers and students respectively. The study also contributes toward filling the gap in the existing literature on assessment practices. Furthermore, it aims to encourage external examination bodies and policy-makers to reflect upon their current policies as well provides suggestions to school teachers and management.