We conducted a systematic review. Systematic reviews try to find all the research that has ever been conducted on a particular topic, then consider what the entire body of evidence can reliably tell us. This helps us to avoid the bias that occurs when people are selective in which research they cite when debating the merits of a new teaching approach. We looked for research that compared the effects of pedagogical translanguaging with English-only approaches on measures of English language proficiency. We also assessed the trustworthiness of the studies that we found, i.e. whether they were conducted to a standard that would allow us to have confidence in their results.

In total, we found ten reports (reporting eleven individual studies) that compared pedagogical translanguaging with English-only approaches. They addressed a variety of different outcomes, such as scores on assessments of English reading, writing, and speaking, as well as more fine-grained outcomes such as understanding comprehension questions that were written in the passive voice. In about half of the studies, pedagogical translanguaging was associated with better English language outcomes than English-only approaches. In about half, English-only and pedagogical translanguaging approaches seemed equally effective. One study found that it appeared helpful for some outcomes but not for others. In our analysis of the quality of the studies we found that most had important limitations. Only two studies were conducted in a way that leaves us confident about their results. The remaining studies were compromised by methodological choices that make it difficult to draw any firm conclusions.

We are not confident that there is enough research of sufficiently high quality to help EFL teachers decide whether a switch to a pedagogical translanguaging approach would be worth the investment of time, energy and resources in terms of English language outcomes. However, given that no study found that it was detrimental to English language proficiency, we think that EFL teachers who are motivated to explore pedagogical translanguaging with their learners should feel reassured that it will not disadvantage them. Indeed, we know of many studies that ask language learners how they feel about pedagogical translanguaging that demonstrate that they like it and feel engaged by it. This may be reason enough to consider adopting the approach, regardless of the uncertainty around its effects on English language outcomes. However, if English language outcomes are the priority in any EFL teachers’ context, they should keep an eye on the emerging research in this area, call for more and better research to inform their practice, and participate in well-designed studies that help reduce that uncertainty.