In the formalized context of ESL/EFL classrooms, code-switching is undoubtedly the most commonly observed phenomenon, where teachers and students alternate between L1 and English for different reasons. This language alternation practice in class, however, is frowned upon by many educators since the introduction of English-only (EO) policy and the complete abandonment of students’ mother tongue in ESL/EFL classrooms. Advocates of EO approach claim that learning is greatly affected by the amount of exposure to the language. In contrast, critics of this approach of ‘teaching English through English only’ see it as an ideological perspective, rested heavily on premature and unexamined assumptions. They believe that the use of L1 or code-switching option, with its beneficial effects, is more than necessary for ESL/EFL students at all levels. This paper therefore reports a study carried out to reexamine the practice of the insistence on English only in terms of its pedagogical effectiveness, desirability and thus offer some practical implications for the ESL/EFL profession, particularly in the English learning and teaching settings at tertiary level in Viet Nam. The method of the study involved a 4-point scale questionnaire with 23 items. The participants were 42 first year intermediate and upper-intermediate English-major students. The findings indicated that EO policy did not secure thorough understanding of the lessons for the majority (70%) of the students in the sample. In addition, approximately two thirds of the students admitted being unable to express their ideas freely and a similar percentage of the sample had difficulty communicating with others in the target language. Regarding students’ attitudes, around 55% of the sampled students were reportedly negative towards EO policy although a considerable majority of 92% acknowledged the value of frequent use of English in enhancing learning. The most noteworthy finding was that roughly 70% endorsed the use of L1 as an auxiliary teaching and learning medium. Pedagogical implications and recommendations are then provided so as to ultimately achieve the authentic learning of English in a near L1-free environment, where full understanding and participation are guaranteed.