The current study uses a Rhetorical Structure Theory (RST) diagnostic tool on text organizing ability to automatically grade the results of sentence-arranging tasks performed by elementary school students. It further analyzes the results to identify the factors of the diagnostic tool that were affected. Our findings are summarized as follows. First, the scores of the items with nuclei were higher than those with no nuclei. Second, the correlation between content classifying and content sequencing areas was quite high, and students with low scores were found to have relatively more difficulty with content sequencing. Third, the higher the number of relations and relation types, the lower the score, and for items with the most diverse relation types, the scores between the relation types were very large. These analysis results have important implications for improving diagnostic tools on text organizing ability.