Objective According to a national survey to school teachers carried out by the Ministry of Education in Japan, 4.5 percent of children in mainstream elementary or junior high schools have some difficulty in learning despite of their normal range of intelligence. It is necessary to make clear the developmental changes of basic reading ability in typically developed children, in order to medically diagnose and support dyslexics.

Methods The primary components of Japanese orthography are phonetic letters (Hiragana) and morpho-semantic symbol letters (Kanji). We established three original Hiragana reading tasks composed of single mora, four syllable words/non-words, and short sentences to investigate the developmental changes in 217 elementary school children aged from 6 to 12 years. Their performance and total articulation time for reading were measured.

Results There was a negative correlation between the articulation time and their school grade. The articulation time was significantly longer in the first graders for the word and short sentence reading tasks. In all tasks, the articulation time gradually shortened as they passed on to the upper grades and reached a plateau at the fifth grade (10–11 years old). Performance in terms of number of errors did not significantly change between the school grades for the single mora reading task, but for the other two tasks, first graders had significantly more errors compared with other graders.

Conclusions These results suggest that our Hiragana reading tasks may be useful to detect children with reading disabilities in the lower school grades.