The purpose of this paper was to examine the educational validity of a scale assessing the metacognitive strategy used by junior high school students when they write argumentative essays. Three researches were carried out. The first study was a prestudy, in which a metacognitive strategy questionnaire comprising writing evaluation items and 60 items selected on the basis of students' reflections was developed. In the second study, the exploratory factor analysis showed that the scale contained four subscales pertaining to the following factors: "the planning stage of writing," "reexamination," "formation of a main opinion," and "exploration value"; these subscales comprised 19 items and were completed by 410 students. In the third study, the educational validity of the scale was examined by correlating it with scales on the course of study, self-efficacy, intrinsic value, and writing anxiety, which were completed by 471 students. These results suggested that the metacognitive strategy scale could help in structuring instructional processes and learning activities including the elaboration of "what was recognized" by using "the manners of recognition".