This study examined whether there is a developmental difference in the emergence of an item-position effect in intelligence testing. The item-position effect describes the dependency of the item's characteristics on the positions of the items and is explained by learning. Data on fluid intelligence measured by Raven's Standard Progressive Matrices (SPM) and data on working memory tasks were collected from both primary school age children (7-8 years old) and secondary school age adolescents (12-13 years old). The item-position effect of SPM was represented and separated from the ability component by the fixed-links model. The results indicated a clear age difference: whereas the item-position effect was observed in the adolescents, it was not found in the primary school children. In addition, separating the item-position effect detected in the adolescents from the ability component led to a larger correlation with working memory than otherwise. These results suggest that age differences in intelligence test performance may not only reflect differences in the general ability but also in the sources of the item-position effect.