Flipped learning is a pedagogical approach in which the traditional way of instruction is inverted by presenting new concepts and subject matters before class and allocating more class time to collaborative, individualized, and differentiated learning. Recently, the use of flipped learning has become popular in the context of learning English as a second/foreign language (ESL/EFL). However, no quantitative synthesis has been conducted on the results of flipped ESL/EFL studies so far. Therefore, with this gap in our mind, we conducted a meta-analysis that consisted of 69 between-subject design studies in the field of ESL/EFL, in which we compared the flipped and lectured-based classrooms in improving students' achievements. In order to interpret the results, we used the field-specific benchmark for L2 research proposed by Plonsky and Oswald (2014) in Mod Lang J 100: 538-553, 2021. We found that the influence of flipped learning on students' achievements was large and positive. Also, the findings of moderator analysis indicated that the flipped group performed better when some extra activities and exercises were accompanied by pre-class materials. We conclude that although flipped learning is new in the ESL/EFL field, it has the potential to improve students' achievements if appropriately designed and implemented. Moreover, since flipped learning is in its fledgling state in the ESL/EFL field, more empirical evidence and research is required in all educational levels to examine its effectiveness, more specifically regarding design and implementation.