This study investigated the longitudinal associations between teacher support (i.e., emotional and instrumental support) and academic (i.e., math) achievement at the between-student and within-student levels using random intercept cross-lagged panel models (RI-CLPMs). Data were collected from 694 elementary school students in China (44.9% girls; M = 10.53 years, SD = 0.70) over four waves across 2 school years. Results from the RI-CLPMs supported that higher academic achievement was significantly associated with higher teacher emotional and instrumental support at the between-student level. At the within-student level, the RI-CLPMs only supported the predictive effect of academic achievement on teacher instrumental support, but not emotional support. Further analysis utilizing cross-lagged panel models (CLPMs) demonstrated significant reciprocal effects between teacher emotional support and academic achievement, as well as instrumental support and academic achievement. No significant sex differences were observed in RI-CLPMs or CLPMs. The findings illustrate the importance of distinguishing the between-student and within-student associations in longitudinal relations concerning teacher support and academic achievement.