This paper provides insights into how participating in an action research study challenged traditional beliefs about teaching practices and led to more active learning strategies being included in English for Specific Purposes (ESP) Science classes at a Vietnamese university. Recent reforms in higher education teaching and learning, by the Vietnamese government, have placed increased demands on universities to employ more active learning approaches to meet future global needs. InVietnam, university teaching has generally been based upon traditional lecturing, whereas active learning requires a more student-centered approach whereby students engage cognitively in learning through increased participation, and take greater responsibility for inquiring into new knowledge in meaningful and critical ways. Using a participatory action research approach, interviews, observations and planning meetings were undertaken with eight Science lecturers who were currently teaching ESP. The findings revealed how the lecturers underwent positive pedagogical shifts from traditional lecturing to more constructivist approaches to teaching and learning over the time of the study.