In order to implement the philosophy of a 12-year basic education, practicing competency-based instruction is necessary. Studies demonstrate that Project-Based Learning (PjBL) is one of the best approaches for competency-based instruction. The purpose of this study is thus to explore PjBL implementation, the effectiveness of constructing content knowledge, and the application and promotion of communication and interaction competency. The research objects are first-year senior high school students. The experimental group (n1=64) underwent PjBL introduced into the sex education module. The control group (n1=57) had a partial lecturing module. The results reveal no significant differences in the independent sample t test of academic achievement between the experimental group and the control group. Introducing PjBL could promote students’ self-directed learning to construct content knowledge. The results also show that introducing PjBL could both promote students’ attention to sex health issues and provide a chance for them to apply and promote communication and collaboration competency/skills. In order to implement PjBL for the first time in the future, practitioners should start with the microcourse module, select high relevant themes, set it up for a single subject or interdisciplinary topic, adopt multiple assessment strategies, and reflect upon the results.