A mixed-methods design (Creswell & Creswell, 2018) was adopted in this action research to examine the effects of reading strategy instruction with four reading strategies - previewing the text, predictions, text-structure awareness, inferencing - on reading performance of non-English majored freshmen in English preparation classes of a private university in Vietnam. Thirty-six students in pre-intermediate English proficiency level participated in the study. Over six weeks, these students received the four reading strategies instruction explicitly in accordance with CALLA model. Via the explanatory sequential design, a type of mixed methods research involves two-phase data collection (Creswell & Creswell, 2018). The results of the pre-post-tests and 11 closed-ended response items in the paper-based questionnaire were analyzed quantitatively while 6 interviews were analyzed qualitatively to provide further explanations of the quantitative results. The study has found that four reading strategies might serve as techniques to improve reading comprehension then result in better reading performance, reading speed and higher frequency of reading strategies use.