Although a variety of collocation tests have been developed so far, all of these tests have some limitations in that they do not measure absolute collocation knowledge. The present study was designed to validate the hierarchy of the Collocation Size Test (CST) developed in Kwark, Shin, & Lee (2019) study to measure the size of the absolute collocation knowledge of 160 Korean elementary students. The CST consists of four levels and each level contains 10 items, representing the knowledge of 500 collocations. The validation procedure of the CST was performed, using the Rash model. In order to validate the CST items, the Wright Map was used to check whether their CST could measure the general collocation proficiency of the subject group and the quality of the items was verified through the item fit. In addition, in order to verify whether the items graded for the four levels of the CST could function hierarchically, the mean score and the 95% confidence interval of the 10 items of each level were analyzed. The findings showed that the hierarchical structure of the four levels is appropriately differentiated.