The purpose of this study was to investigate the effect of the "knowledge of cognition" and "regulation of cognition," which are processes of the metacognitive strategy for improving learners' writing skills. The working group for the present study, in which a sequential explanatory design was employed, included 44 pupils (21 control, 23 experimental) at a private secondary school. The pupils in the experimental group were instructed in metacognitive strategy-based writing practices, whereas the pupils in the control group were instructed in traditional writing practices. The results revealed that it is necessary to effectively use the metacognitive strategy in learning and teaching to improve writing skills. Further experimental research is recommended to determine, using various scales, whether the metacognitive strategy influences writing skills.