This study explores the transformative impact of metacognitive strategy instruction on the speaking proficiency of Iranian advanced English as a Foreign Language (EFL) learners, particularly those preparing for the IELTS exam, by comparing it to conventional teaching approaches. Grounded in self-regulated learning theories (Flavell, 1979, pp.906-911; Zimmerman & Schunk, 2009), metacognitive strategies—encompassing planning (e.g., goal-setting and concept mapping), monitoring (e.g., self-correction via checklists), and evaluation (e.g., reflective assessments)—empower learners to regulate their cognitive processes, fostering greater autonomy and communicative competence in high-stakes contexts where speaking anxiety is prevalent, such as among Iranian test-takers influenced by cultural factors like collectivism and test-related stress (Hofstede, 2011; Hosseini, 2020, pp.29-48). Employing a quasi-experimental mixed-methods design, the research involved 100 conveniently selected Iranian IELTS candidates (50 males and 50 females, aged 18-25) from language institutes. Participants were stratified by gender and proficiency, then randomly assigned to two groups of 50 each. Initial equivalence was ensured via the Oxford Placement Test (OPT), with no significant differences (t(98)=0.42, p=0.68). The experimental group underwent an 8-session intervention integrated into a 36-session IELTS course, featuring explicit training in metacognitive strategies through mini-lessons, guided practice, and tools like graphic organizers and reflection sheets. The control group received traditional instruction emphasizing repetitive drills, model answers, and error correction. Data collection included pre- and post-intervention speaking assessments via audio-recorded conversational tasks on familiar, engaging topics (e.g., technological innovations or family roles, with one on recent social events for authenticity), scored on a 0-20 scale adapted from IELTS descriptors for fluency, accuracy, and lexical resource (inter-rater reliability: Cohen's Kappa=0.85). Supplementary measures comprised the Metacognitive Awareness Inventory (MAI) for awareness levels and immediate recall interviews for qualitative insights into self-assessment processes. Results revealed statistically significant enhancements in the experimental group's speaking skills, with a mean post-test gain of 1.65 points (from 6.25 to 7.90, SD=0.75-0.85; t(49)=11.46, p<0.001, Cohen's d=2.21), far surpassing the control group's modest 0.40-point improvement (from 6.15 to 6.55, SD=0.75-0.85; t(49)=1.46, p=0.149, d=0.26). Between-group post-test differences were substantial (t(98)=9.34, p<0.001, d=1.89), with ANOVA confirming main effects across components: fluency (F(1,98)=87.19, p<0.001, η²=0.47), accuracy (F=82.45, p<0.001, η²=0.46), and lexical resource (F=65.78, p<0.01, η²=0.40). MAI results showed gains in regulatory skills for the experimental group (M increase=0.45, p<0.01, d=0.59), while qualitative themes from interviews highlighted increased planning confidence (78% of participants), real-time error correction (65%), and cultural alignment with collaborative reflection. These findings affirm the pedagogical superiority of metacognitive instruction over traditional methods in EFL contexts, addressing a research gap in Iranian IELTS preparation (Heidari Vincheh et al., 2024). Practical implications include recommendations for educators to adopt the "P-M-E Cycle" (Plan-Monitor-Evaluate) in classrooms, for curriculum developers to integrate strategy modules into materials, and for learners to build self-efficacy. Limitations, such as the intervention's brevity and potential topic sensitivity, suggest avenues for future longitudinal, multi-site studies. Ultimately, this research underscores metacognition's role in cultivating resilient, autonomous speakers, enhancing communicative outcomes in diverse cultural settings.
