Teacher is the most important element in raising students' performance. Considering this notion, many organizations/schools conduct professional development programmes for its teachers within the school context, to change their attitudes and to enhance their capabilities. This study explored how a professional development programme conducted by ABC organization enhanced teacher quality and performance. The findings reveal that in-house professional development has enriched teachers' content knowledge and instructional experiences. Moreover, it has also developed their classroom management skills. Schools should plan and administer professional development programmes for improvement and teaching learning process. Apart from conducting these sessions, schools should also provide opportunities to implement learning from the professional development activities in the actual classroom like this school. The school is providing technical and administrative support in implementing learning from professional development sessions. However, there are also some factors that are deterring the implementation of teachers' learning in actual classroom teaching. For instance, the large class sizes and the intensification of work is a big challenge for teachers. This study recommends that professional development should focus on teachers' and students' needs. It should relate to actual classroom situations. Keywords: Influence, Professional development, In-house professional development.