This study sought to examine the link between social physique anxiety and positive and negative affect experienced during physical education (PE) classes as well as the moderating roles of gender and school level in these relations. Participants were 522 students ranging from the fourth grade of elementary school to the third grade of middle school in H City, Gyeonggi Province, South Korea. They answered two questionnaires between November and December 2025: the Social Physique Anxiety Scale and selected positive and negative affect items from the Positive and Negative Affect Schedule-X. The collected data were then subjected to confirmatory factor analysis, reliability analysis, independent-samples t-test, one-way analysis of variance, and hierarchical regression analysis in SPSS 26.0 and AMOS 24.0. Results showed that male students reported higher positive affect than female students, while female middle school students displayed higher social physique anxiety. Significant differences across grade levels were also observed. Social physique anxiety was negatively associated with positive affect and positively related to negative affect. Moreover, for both types of affect, significant three-way interaction effects among social physique anxiety, gender, and school level were identified. These findings indicate that the interaction between psychological and contextual factors drives emotional experiences in PE. Hence, educational efforts should aim to reduce body-related anxiety and create more supportive and inclusive PE environments.