Trained intensively in teaching English for communication, beginning Vietnamese ESOL teachers still follow the traditional approach in their classroom, i.e., teaching for grammar-and-vocabulary exams. This contrast in pedagogical practices is caused by "reality shock", which happens for most teachers during the first few years into teaching. The current study aims to explore how reality shock influences and transforms early career ESOL teachers' teaching methodologies. It employs an interpretative case study research design to outline both external and internal factors that characterize reality shock. The results show that besides English education policy, students' cooperativeness and professional support, the participants were also affected by their own pedagogical competence, beliefs, and attitudes. Recommendations for assessment policies, professional development and further research have also been put forward.