This research aims to evaluate the impact of Continuing Professional Development (CPD) for in-service primary teachers on educational quality in the service area of Salavan Teacher Training College (Salavan and Sekong provinces), while proposing methods to improve the effectiveness and sustainability of teacher behavioral change. A Mixed Methods approach was utilized, employing questionnaires with 185 teachers, in-depth interviews with 20 administrators, and classroom observation of 15 teachers. This methodology facilitated Triangulation across teacher perceptions, administrator perspectives, and actual teaching practice. The statistical measure employed is the mean. Key Findings: • Model Effectiveness: Teachers reported that Job-Embedded Learning and Professional Learning Communities (PLCs) were the most effective models ( =4.45), confirming initial improvement in teaching skills for addressing Adaptive Challenges (e.g., multigrade teaching). • Systemic Gap (The Broken Loop): The greatest structural deficiency was found to be the post-training follow-up support, which scored lowest ( =2.50). This failure prevents the Continuation phase of change (Fullan's theory), leading to an incomplete Reflective Practice cycle for teachers. • Implementation Gap: Classroom observation confirmed that the use of ICT/Technology ( =2.55) and Formative Assessment ( =3.10) remains low in actual teaching practice, despite a high reported need for TPACK competency. The training showed good initial impact, but long-term effectiveness is limited by the lack of a sustained follow-up mechanism. It is recommended that the Ministry of Education and Sports (MoES) allocates dedicated budgets for CPD follow-up and that the Teacher Training College designs ADDIE Model curricula that embed TPACK into Lesson Study, utilizing the existing Virtual Coaching (WhatsApp) mechanism systematically to close the learning loop and ensure quality based on Data-Driven principles.