In this study, causal factors involved in Kanji reading difficulty among second to sixth graders (N=4519) were examined by employing tests that comprised reading Kanji words, rapid searching of Hiragana words, writing special morae, verbal short-term memory, verbal working memory, and visual short-term memory. CHAID analysis showed that second to fourth graders with special morae test scores below the 10th percentile had the lowest Kanji reading ability in their grades. Furthermore, children with scores below the 10th percentile in the rapid searching of Hiragana words test had poor Kanji word-reading ability. Fifth and sixth graders with scores in the verbal short-term memory and/or verbal working memory tests below the 10th percentile had the lowest Kanji word-reading ability in their grades. The results suggest that the first causal factor among second to fourth graders may include low performance in phonological awareness. Furthermore, the first causal factor among fifth and sixth graders could be linked to poor verbal memory.