The primary purpose of this study was to understand how teachers develop and work as agents of change. The particular aim was to understand the impact of SST program on teachers' classroom practices. An attempt has been made to explore how extensive in-service teacher development programs have an impact on teachers' classroom practices. The study documents the cases of two secondary teachers (who have attended the SST program) from two different contexts (government and private schools). The research draws on qualitative data from sources such as semi-structured interviews, classroom observations and document analysis. The teachers (SSTs), head teachers, fellow teachers, SSTs' students, the course coordinator, and the PDT who was involved in the SST program were interviewed. A number of lessons of both the teachers (SSTs) were observed. Although the study is based on the analysis of only two cases, it provides some insight into the process of teacher development. The SST program has a great impact on teachers' classroom practices. Positive changes were noted in SSTs' classroom practices. However, there is still need for further AKU-IED based support. Moreover, it is necessary to build a school culture and structure that is conducive for the sustainability of the innovation. The study suggests that a professionally trained teacher cannot bring change without a support system. The study also revealed that there was a lesser impact on government school teacher's classroom practices, as compared to the private school teacher, because of a number of factors. In brief, this study reveals that any professional development is not an isolated station in an individual's intellectual journey, but rather a gradual process. The study has also made some recommendations for the schools and for AKU- IED for the improvement of teacher education programs.