Educational reforms in many Asian countries, particularly in China and Vietnam, have highlighted the pivotal role of the constructivist approach. However, the implementation of constructivism into the classroom is still very challenging for teachers. Although there is a wealth of research on constructivism, few studies have focused on the difficulties teachers often encounter when organizing constructivist lessons, especially in the EFL context. To address this gap, this study employed a mixed-methods approach, including triangulated data (a questionnaire, classroom observations, and semi-structured interviews) with the participation of 120 EFL teachers in a private university in Vietnam. The findings indicate that teachers faced a wide array of problems in their constructivist classes, including conceptual, pedagogical, cultural, political, and technological dilemmas. Furthermore, they did not comprehend constructivism as they believed, probably due to a superficial understanding of this approach or the effect of Confucian culture. Additionally, this study verifies and contributes to the framework of Windschitl regarding the four dilemmas teachers often confront in constructivist classrooms. Theoretical and practical implications for future researchers as well as for educational stakeholders and institutional leaders on what should be taken into careful consideration prior to the incorporation of constructivism, were also discussed in detail. Purpose: explore the difficulties teachers often encounter when organizing constructivist lessons, especially in the EFL context. Methods: employ a mixed-methods approach, including triangulated data (a questionnaire, classroom observations, and semi-structured interviews) with the participation of 120 EFL teachers in a private university in Vietnam. Findings: 1. Teachers faced a wide array of problems in their constructivist classes, including conceptual, pedagogical, cultural, political, and technological dilemmas. 2. Teachers did not comprehend constructivism as they believed, probably due to a superficial understanding of this approach or the effect of Confucian culture. 3. The framework of Windschitl is still applicable to today's educational context regarding teachers' difficulties in constructivist classes. Technological dilemmas should also be taken into consideration. Implications: 1. Thorough training on constructivism for teachers is highly needed to assure the successful implementation of this approach. 2. The curriculum and assessment should be modified in correspondence with the constructivist approach. 3. In-depth orientations are needed for both teachers and students to comprehend their expected roles. 4. Technological tools should only be used when necessary to avoid students' distraction. Limitations: 1. Small sample size 2. EFL context only 3. Individual differences (age, years of teaching experience, etc.) not taken into consideration.
