This is the study to report Japanese two-year longitudinal reading amount data using the Title Recognition Test (TRT) and school book borrowing (the number of books borrowed from a school library) as measures elucidating the relationship between reading amount and Japanese letter reading skill. We found separate, significant positive effects for the reading amount indices on letter reading skill both one and two years later. For the longer duration, both indices had almost the same effect. We concluded that extensive reading increases knowledge of Japanese letters (in particular, the knowledge of the connections between hiragana and kanji). In addition, distinctive features of both indices of reading amount-TRT and school book borrowing-are discussed; school book borrowing, in particular, has not been used as an index of reading amount in previous studies, so we assert its utility here.

Key words: letter knowledge, longitudinal studies, school libraries, print exposure, kanji