The study explored teacher performance appraisal and the potential benefits of appraisal as a mechanism for improving existing performance of teachers to collaboratively implement changes that lead to improve practice. The purpose of this Participatory Action Research (PAR) was to improve the existing documents and practices of teacher performance appraisal system and practices at a Community Based High School (CBS) in Karachi through collaboratively involving the principal and teachers in a systematic process of improvement. The research was qualitative in nature using PAR model as suggested by Kemmis and Mc Taggart (2000). This PAR model provided opportunities of constantly evaluating the teaching and learning strategies and their implementation in a real setting. The data of the study was collected through interviews, classroom-observations and feedback processes, assessments tools, field notes, reflection of research participants and document analysis to obtain empirical evidence of existing practices and perceptions. The findings were processed through data analysis by arranging data systematically and breaking it into units through coding, in order to meaning making of the data. The findings of research revealed that the awareness about the appraisal system and process is indispensable to improving the practices and understanding of the teachers. Moreover, it emerged from the findings that timely feedback, involvement, trainings and evaluation of set targets acted as cornerstones to improve the practice and process of the appraisal system. The findings reveal that the awareness training programmes regarding appraisal system enhance the knowledge and skills of teachers if the appraisal documents are understood by the teachers. Further research revealed that involvement of teachers in developing appraisal documents creates a sense of ownership, and this feature helps to improve the practices. The two purposes of appraisal, i.e. accountability and professional development, may not be segregated from each other at CBS; however, the focus of appraisal system shifted from accountability to professional development. This study holds significance for various audiences directly or indirectly, such as CBS where I carried out this research, and my own organization which I work for. The study could help in strengthening the appraisal system and process and it could also enable principals in further improving their appraisal system and practices. The recommendations that have come from this research are that school leadership should involve the teachers in making policies and procedures so that the teachers feel ownership of the appraisal system. The process of appraisal should be strategies in such a