This cross-sectional study assessed quantitative differences in school student traffic accident injuries and fatalities during commuting to school and private traffic according to students’ year of study in school.　We created the working hypotheses presented below.

　・Immediately after entering a higher grade at a different school, student patterns of school commuting and private daily life activities extend and vary.　The different activity patterns engender sudden increases in opportunities for passage through new and unfamiliar road environments, thereby increasing student traffic casualties.

　・As school years advance, students gradually learn and become accustomed to new road environments.　In addition, their cognitive functions develop gradually.　These bring a gradual decrease in student traffic casualties.

　Using a Japanese national traffic accident database, the numbers of student casualties per 100,000 population during April 2013-March 2018 were analyzed for students of elementary school through senior high school.　A tendency showed that student casualties during the first year after entering a school of higher grade were more numerous than those of the prior academic year. Student casualties became fewer as the school years advanced.　These results partially support the hypotheses presented above.