Attentional control indexed by intraindividual reaction time variability (IIRTV), which is found a crucial predictor of children's academic performance, may also be influenced by children's academic achievement. However, the bidirectional longitudinal relationships between children's IIRTV and academic achievement remain unclear. This study aimed to examine this issue in 211 Chinese primary school children (98 girls; Mage = 7.39 years, SDage = 0.49). Children's IIRTV was assessed using the flanker task - child version in three waves from the first to the third grade, and the children's final grades in Chinese and math for each year were collected from the school. The results showed that (1) IIRTV to the flanker task decreased with age; (2) IIRTV and Chinese achievement had a bidirectional longitudinal relationship, suggesting that IIRTV predicted prospective Chinese achievement; and Chinese achievement also predicted subsequent IIRTV in children. These findings have implications for promoting children's attentional control and academic performance.