This study investigated the impact of structuring and problematizing scaffolding mechanisms on 240 Iranian English as a foreign language learners' individual and socially shared metacognition in writing skills. The study also sought to find out whether the learners' proficiency level moderated the effect of the scaffolding mechanisms on metacognition at the intra- and interindividual levels. The results of a 2-way analysis of covariance, 4 Kruskal-Wallis tests, and 2 chi-square tests revealed that providing learners with either structuring or problematizing scaffolding mechanisms led to significant improvements in both learners' individual and socially shared metacognition. The results also indicated that when structuring and problematizing scaffolding mechanisms were offered simultaneously, they functioned more effectively in terms of increasing learners' metacognition at both the intra- and interindividual levels. Moreover, according to the findings of this study, learners' level of proficiency did not moderate the effect of scaffolding mechanisms on individual and socially shared metacognition.