Acknowledged as a far-reaching pedagogical method, Project-Based Learning is nationally imperative in Indonesian education despite the disinclination of its execution. This paper scrutinizes the phonetics and phonology-based English pronunciation dimensions and scaffolding traits as the bases to devise the scaffolding assignments for PBL execution, explores the process of PBL with scaffolding assignment adoption, and examines whether the exertion of the PBL enhances the academic achievement of English pronunciation and autodidacticism as Self-Directed Learning skills. The study exploits design-based research through repetitive actions of analysing, designing, developing, implementing, and evaluating. The result exhibit that the scaffolding assignments are designed by decomposing the phonetics and phonology pronunciation-related conceptions into smaller tasks of English pronunciation learnings and trainings based on instructional scaffolding fundamentals. The scaffolding assignments infused PBL is applied through orientation, action, reflection, and presentation stages which cover the learning activities of launching the project as the entry event marked with the driving question disclosure; building knowledge, understanding, and skills to answer the driving question; developing the project products and answers to the driving question; and presenting the products and answers to the driving question. The exertion of the PBL with scaffolding assignments is proven influential in promoting the students' English pronunciation and SelfDirected Learning skills.