Research shows that assessment plays a pivotal role in the teaching learning process. While some forms of assessment enhance teaching learning, others may inhibit it. Focusing on assessments, Aga Khan University Examination Board (AKU-EB) was established in 2003 to offer SSC certificate at the end of secondary schooling under the National Curriculum. Its objective was to restore the deteriorating standard of SSC certificate offered by schools affiliated with the Public Examination Boards. Many of the schools affiliated with the Public Board have shifted to the AKU-EB board after its inception. This study was conducted in order to seek to understand how changing from the Public Board to AKU-EB effects the curriculum of a private school in Karachi, Pakistan. In order to achieve this purpose, a case study approach in the qualitative paradigm was adopted. The research drew on semi-structured interviews of various stakeholders, including the Principal, teachers and students, classroom observations and document analysis as the sources of data collection. The study findings revealed that the AKU-EB examination assesses the students, on the basis of the student learning outcomes (SLOs) of the National Curriculum at three cognitive levels - knowledge, understanding and application - rather than a prescribed textbook. This has been a major driving force for change. The teachers refer to multiple sources of information and the students are all familiar with the SLOs as prescribed in the examination syllabus. The study showed that there has been a major impact on the school curriculum by the change in the examination methodology. These effects, among others, include a paradigm shift in the teaching approach from traditional teaching to student-centered learning, opportunities for subject content integration, and students moving towards becoming independent self- learners. The teachers have moved towards collaborative lesson planning, and there is development of a positive teacher-student relationship. The study also showed that there has been a ripple effect on the lower secondary school curriculum. In the light of these findings, the study also makes recommendations and suggestions for future research.