RESUMEN
This study strove to investigate the effect of L1-mediated metacognitive intervention (MI) on the listening comprehension performance, metacognitive awareness, and motivation of Iranian EFL learners. The participants were 330 upper-intermediate EFL learners in three groups, ranging from 17 to 25 years of age. The experimental groups (Ex1 = 110/Ex2 = 110) went through a guided lesson plan in metacognition in L2 (English) and L1 (Persian) for seventeen weeks, which focused on planning, monitoring, and evaluation. The control group (CG = 110), also instructed by the same teacher, listened to the same texts in L2 (English) without any guided attention to process. An actual IELTS TEST, the Metacognitive Awareness Listening Questionnaire (MALQ) and a motivation questionnaire (LLOS-IEA) were used before and after the intervention to track changes in the listening performance, metacognitive awareness, and motivation. The overall results showed that MI caused a considerable variance in the listening performance, metacognitive awareness, and motivation in both experimental groups. The results also illustrated that the medium for the delivery of metacognitive intervention (L1) assisted the learners in experimental group two, who went through L1-mediated metacognitive intervention, to outperform their peers in experimental group one, who were taught in L2, and the control group, who were taught conventionally.