Book‐Reading Time Is Consistently Associated With Higher Vocabulary Growth Across Elementary, Middle, and High School

Abstract Using data from the Japanese Longitudinal Study of Children and Parents, we tested whether time spent reading books predicts vocabulary growth and whether this association varies by school level. Overall, we analyzed the data of 1,469 elementary (Grades 4–6), 1,300 middle school, and 1,362 high school students. Vocabulary was assessed using tests based on item response theory, administered at Time 1 (2017) and Time 5 (2020), which are comparable across school levels. Daily book‐reading time was reported at up to three interim waves. Moreover, we used latent change score models to examine three‐year vocabulary growth while controlling for 11 activity and demographic covariates. Multigroup invariance tests favored a model in which the path from book‐reading time to vocabulary growth was constrained to be equal across the three school‐level groups, and this common path was significant. These findings suggest that book‐reading instruction should be systematically implemented and strengthened in elementary, middle, and high schools to sustain and support vocabulary development across grades.