Prior research with adult participants reported a rightward bias in the reading version of the flankers task. Here we investigated how this bias evolves as a function of reading expertise. We tested two groups of French primary school children from Cycle 2 (grades 1 & 2) and Cycle 3 (grades 4 & 5), and one group of adult participants. In the related flanker conditions the central target word was flanked by the same word either on the left (park park ####), the right (#### park park), or on both sides (park park park) – referred to as the “bilateral flanker” condition. In the unrelated conditions, the repeated flanker words were replaced by a different unrelated word. In the analysis of standardized RTs, there was a three-way interaction between the three groups of participants and the impact of flanker relatedness as a function of the position of the related flankers. This three-way interaction reflected the significantly greater increase in effects of flanker relatedness between Cycle 2 and Cycle 3 for the bilateral flanker and the right flanker conditions compared with the left flanker condition. This suggests that the rightward bias is driven by attentional asymmetries that develop during the process of learning to read.