The role of headteachers in the school improvement process has been considered crucial, both in developing and developed countries but no effective measures have been made by the government and other private educational agencies in Pakistan to develop their skills, knowledge and attitude. Acknowledging the importance of headteachers' role in education system, the Aga Khan University, Institute for Educational Development (AKU-IED) launched Advanced Diploma in School Management (ADISM) for the professional development of working and aspiring headteachers in cooperating schools. The study was conducted in two AKU-IED's cooperating schools to understand the headteachers' perceptions about the impact of the ADISM programme towards enhancing understanding of their roles and responsibilities. A variety of research methods such as interviews, observations and document analysis were used for the purpose of collecting rich data. Different tools of data collection were used to triangulate the data to ensure the purpose of validity and objectivity. The findings suggest that the ADISM programme has contributed substantially towards enhancing headteachers' understanding of their role as pedagogical leaders. This allowed them to assist teachers in curriculum enrichment and enhancing their instructional strategies. It reveals that, both the headteachers acquired knowledge about school improvement process such as teachers' empowerment, developing schools' shared vision and designing strategic plans to realize the vision. The study shows that the ADISM programme has also contributed towards changing the headteachers' leadership style. Both the headteachers have developed a culture of professionalism in their schools in one way or other. However, the degree of implementation of newly acquired knowledge and skills of headteachers found to be different in either context due to various contextual factors.