This thesis aims at investigating the beliefs of seven English high-school teachers about constructivist teaching and their classroom practices at a high school in a Northern area of Vietnam. Its purpose is to illuminate the conditions affecting their ability and willingness to reform teaching practices at their schools. Three distinct groups of participants are identified: Traditional Conservers, Neutral Pragmatists, and Adaptive Originators. For the Traditional Conservers, beliefs about teaching were strongly teacher-centered, supportive of traditional education methods, and shaped by beliefs that students should be obedient and passive learners. These participants had a limited understanding of the range of approaches to constructivist teaching: they were unwilling to change how they activate constructivist teaching in practice. For the Neutral Pragmatists, however, the need to reform teaching practices was recognized. These participants expressed a willingness to change their own teaching practices, but they felt constrained from doing so because of a perceived lack of expertise and because they saw that many more hours of work would be required to do so effectively. This group, therefore, had implemented a few significant changes. The Adaptive Originators aspired to reform how teachers utilized constructivist teaching in practice: they actively implemented measures to achieve effective reform. They were more inclined than any other participants to value the importance of constructivist teaching. They also claimed to be strongly supportive of the role and significance of constructivist teaching.