Participating in effective professional development (PD) activities is crucial for helping teachers improve the quality of pedagogy and students' learning results. Numerous factors influence the design of effective PD, one of which is duration. However, many teachers do not find much time to participate in long-term concentrated and continuous PD due to their heavy workloads. Based on this consideration, this paper presents the Workshop-Seminar-Demonstration Class PD (WSDPD) model, which addresses the factor of duration by shortening the hours of contact, lengthening the total span of time required, and integrating elements such as active learning and expert follow-up to improve teachers' practical teaching methods. With "Teaching for Conceptual Change" as the theme and junior high school science teachers as participants, the results of the study show that WSD-PD can serve teachers by generating willingness to improve teaching practices for and influence teaching behaviors in them. The settings of different activities in this model are also considered to play distinct and indispensable roles in the program.