<p>Teacher academic and emotional support play a crucial role in students’ reading achievement, yet the underlying mechanisms remain underexplored. Utilizing data from PISA 2018, this study investigates how school belonging moderates the indirect effects of teacher academic and emotional support on reading achievement via mastery goal orientation. Based on a sample of mainland Chinese students (<i>N</i> = 12,058), the findings indicate that: (a) both academic and emotional teacher support positively predict reading achievement; (b) mastery goal orientation mediates these relationships; and (c) contrary to expectations, school belonging negatively moderates the indirect effects – the indirect effects are stronger when school belonging is low. For academic support, the first‑stage interaction (support → mastery) was significantly negative, whereas for emotional support, neither path interaction reached significance; nevertheless, the overall indices of moderated mediation were significant for both models, indicating that the joint contribution of the two stages (weighted by the strong main effects) produces a reliable change in the indirect effect across levels of belonging. These results challenge the assumption that belonging universally amplifies the benefits of teacher support and instead suggest a buffering role of belonging in the Chinese educational context. The findings highlight the importance of providing targeted support to students with low belonging and call for culturally sensitive models of motivation and achievement.</p>