This study examined the influential factors toward conceptual changes in in-service teachers as they engaged in a summer professional development program. The program curricula attempted to challenge teachers over weaknesses in their pedagogical instruction, provide feasible teaching approaches, and cultivate their strengths and interests through action research projects. A variety of data sources including documents, interviews, and researcher-developed questionnaires were collected and analyzed for reflecting on the effects of remodeled curricula. Findings indicate that the in-service teachers' abilities, their prior views of the nature of students' learning, science teaching and the science discipline, and social factors impede teachers from adopting constructivist teaching approaches. (DDR)