Engaging in continuous professional development (CPD) is crucial for teachers to enhance their learning and teaching quality. A large-scale training has been debated as a one-stop training, while the investment's value remains debatable. This study examined the impact of a large-scale training program called the Bootcamp, organized in Thailand, on teachers' development through the analysis of questionnaire responses, interviews, and observations of teacher training activities. The findings reveal that the initial training led to the arrangement of several projects that utilized the resources of the initial project and facilitated the teacher development, as well as teacher trainers and support personnel. Furthermore, the training generated an indirect impact through the establishment of networks and collaboration in various forms, although ongoing support and encouragement are still required to transform these networks into sustained collaboration. The findings highlighted the importance of comprehensive long-term planning by stakeholders, including policymakers and CPD providers, to align immediate, follow-up, and future activities, foster collaboration through teacher networks, and leverage practical and cost-effective approaches like Professional Learning Communities (PLCs) to promote long-term impact on teacher development.