A study was conducted to examine the significance of "momentum" in physical education classes. The term "momentum" means the percentage of learning engagement in the motor learning episodes of physical education classes. A new instrument was developed to assist with the observation of momentum. In order to examine the significance of momentum in physical education classes, the relationship between learning engagement and students' formative evaluation of physical education classes was analyzed. Sixty physical education classes in 16 elementary schools were investigated, and the main results were as follows : 1) The total time of PE content and motor learning episodes showed significant positive correlations with formative evaluation scores. In contrast, the total time of management episodes had significant negative correlations with formative evaluation scores. 2) The percentage of learning engagement, especially motor learning engagement, showed significant positive correlations with formative evaluation scores. Conversely, the percentage of nonlearning engagement, especially off-task behavior, had significant negative correlations with formative evaluation scores. 3) These results suggest that momentum in physical education classes is positively related to students' evaluation. Thus, it is reconfirmed that momentum is one of the most important factors for producing effective physical education classes. 4) It was also confirmed that the observation instrument used in this study is effective for evaluating momentum in physical education classes.
