Based on Fredrickson's Broaden-and-Build Theory of Positive Emotion, we explored the role of school affect (i.e., positive affect in school and negative affect in school) in connecting gratitude, prosocial behavior, and school satisfaction among a sample of 324 (176 males) elementary school students in grades 4 to 6 by using structural equation modeling. The participants completed a packet of questionnaires, including the Gratitude Questionnaire (GQ-6), the Elementary School Students' Subjective Well-Being in School Scale (ESSSWBSS), and the Primary School Upper Grade Students' Prosocial Behaviors Questionnaire (PSUGSPBQ). The results showed that elementary school students' (1) positive affect in school and negative affect in school significantly related to school satisfaction; (2) prosocial behavior fully mediated the relation between gratitude and school satisfaction; (3) gratitude related to school satisfaction indirectly through positive affect in school and negative affect in school. As hypothesized, the effect was stronger for positive affect in school. Limitations and practical applications of the study were discussed.