This study investigated the quality of metacognition at its inter-individual level, i.e., socially-shared metacognition, across two collaborative writing tasks of different difficulty levels among a cohort of Iranian EFL learners. Moreover, it examined the correlation between the individual and the social modes of metacognition in writing. The analysis of think-aloud protocols of a number of pre-intermediate and advanced EFL learners revealed instances of episodes in which peers used metacognitive activities at pair level. Besides, comparing think-aloud protocols of tasks indicated more frequent and longer use of socially-shared metacognitive episodes in more difficult writing tasks. The study also found high correlation between the social mode of metacognition in L2 writing and learners’ individual metacognition. The pedagogical implications include the provision of learning opportunities in which learners are challenged to exploit metacognitive strategies, such as planning, monitoring, and self-evaluating.