This study examined the effect of a physical education game, created on the basis of self-determination skill, to underachievers. Forty two underachievers participated in this study, all of whom were fifth graders in six different classes of C elementary school in Incheon. The participants were divided into two groups: One is the experimental group and the other is the control group. Twenty one students in three different classes participated in each group. The number of games in the fifth-year physical education reaches eleven, mainly developed from sports such as soccer, basketball and hockey. The control group participants were taught following the fifth-year physical education syllabus. In addition to the formal syllabus, choice-making, goal setting, and self-evaluation were inserted for the experimental group participants. According to the findings of the study, self-determination ability of the experimental group participants showed a significant improvement. Sub-factors of self-determination such as autonomy, self-adjustment, psychological ability, and self-realization improved meaningfully. The findings also demonstrated that choice-making, goal setting and modification, and the evaluation process have a positive influence on the self-determination ability of the experimental group participants. The present study is also significant in that subject-matter class in the inclusive environment contributed to the self-determination of underachievers. Key Words : Self-Determination, Physical Education, Game, Underachievers, Inclusion