This study explored the influence on teachers' beliefs about the nature, learning, and teaching of science during a Secondary Science Visiting Teacher Program (VTP). The multiple case study design involved four Visiting Teachers (VTs) from different geographical sites and from different educational sectors i.e. Government and AKES, as the study participants. The Secondary Science VTP offered by the Aga Khan University Institute for Educational Development (AKU-IED) was an eight-week in-service professional development program for secondary science teachers which exposed the VTs to contemporary methods of teaching and learning in science. During the program, course participants were, in particular, introduced to a highly interactive approach to learning and teaching science. For the data collection, a variety of methods were used consisting of interviews, observations, post-lesson discussions, informal conversations, and document analysis. The research participants' beliefs were elicited before and during the later stage of the program using the earlier mentioned methods. It was found that all four VTs began the program holding a highly positivist view about the nature of science and regarded science largely as a body of knowledge comprised of facts and truths. No apparent or measurable change in their views about the nature of science was found as a consequence of having participated in the program. The study found that, although the VTs entered the program holding traditional beliefs about the learning and teaching of science, there was evidence of a noticeable shift in the respondents' beliefs from a transmission mode to one which was more constructivist in nature. That is, at the end of the program, the study participants viewed learning as a more active process whereby learners construct their own personal knowledge about science. Further, the program incorporated many strategies to facilitate conceptual change and appeared successful in challenging the VTs' incoming beliefs about the learning and the teaching of science. The study is seen to hold considerable implication for teacher education in other subject areas. Several recommendations for further research are presented in light of the study findings.