Purpose <p>This longitudinal study examined the reciprocal relationships among perceived teacher support, peer support, and student engagement in middle school physical education classes.</p> Methods <p>Using a two-wave panel design, data were collected from 477 Chinese middle school students at two time points: Wave 1 (Time 1, T1) in November 2022 and Wave 2 (Time 2, T1) in May 2023, with a six-month interval representing a typical academic semester. This temporal spacing allows for observing developmental changes while minimizing seasonal effects on physical activity patterns. Participants completed validated measures of teacher support, peer support, behavioral engagement, and emotional engagement. Data were analyzed via cross-lagged structural equation modeling to test bidirectional pathways while controlling for grade and gender.</p> Results <p>(1) Behavioral engagement at T1 positively predicted teacher support (<i>β</i> = 0.22, <i>p</i> &lt; 0.01) and peer support (<i>β</i> = 0.19, <i>p</i> &lt; 0.01) at T2. (2) Emotional engagement at T1 positively predicted teacher support (<i>β</i> = 0.22, <i>p</i> &lt; 0.01) and peer support (<i>β</i> = 0.21, <i>p</i> &lt; 0.01) at T2. (3) Peer support at T1 positively predicted emotional engagement (<i>β</i> = 0.16, <i>p</i> &lt; 0.01) and teacher support (<i>β</i> = 0.14, <i>p</i> &lt; 0.05 for behavioral model; <i>β</i> = 0.17, <i>p</i> &lt; 0.01 for emotional model) at T2.</p> Conclusion <p>These findings reveal a spillover effect wherein student engagement fosters subsequent social support, and peer support reinforces both emotional engagement and teacher support. The study underscores the importance of pedagogical strategies that promote active learning and peer interaction, such as cooperative activities and student-centered tasks, to create mutually reinforcing cycles of engagement and support.</p>