AimThe present study aimed at developing a novel scale, the Japan Ijime Scale (JaIS), to measure bullying in Japan with substantial reliability and validity, with which we estimated the prevalence of bullying among children and adolescents of school age.MethodsThe JaIS is a self‐report questionnaire and consists of three parts: subscales measuring victimization and witnessing, and an item measuring perpetration. To test the reliability and validity of the two subscales, the authors analyzed responses to the JaIS from 2334 school students (Grades 4–9) in six elementary and three junior high schools in a middle‐sized industrial city in central Japan, using exploratory factor analysis, item response theory, and examination of the external validity of the items. The prevalence of bullying victimization, witnessing, and perpetration was estimated.ResultsItem response theory models revealed that both the Victimization and Witness subscales have sufficient discrimination power and measurement precision, and the external validity of each scale has been confirmed. Using the JaIS, we found that 35.8% of students had been victims of bullying every 2–3 months (27.6% were solely victims and 8.3% were bully/victims), 32.8% had witnessed some type of bullying act, and 11.8% had perpetrated some type of bullying (3.5% as perpetrators, and 8.3% as bully/victims).ConclusionThe JaIS is a reliable and valid measure. Using this scale, we found a high prevalence of bullying victimization in Japanese schools.

School climate is a significant determinant of students’ behavioral problems and academic achievement. In this study, we developed the Japan School Climate Inventory (JaSC) to see whether it measures school climate properly. To do so, we investigated whether or not the measurement with JaSC varies across sub-groups of varying grade and of gender and examined the relationship between the perception of school climate and the psychological and behavioral traits at individual levels in a sample of Japanese elementary and junior high school students (n = 1399; grade 4–9). The results showed that the measurement was consistent, since single-factor structures, factor loadings and thresholds of the items were found not to vary across sub-groups of the participants. The participants’ perception of school climate was associated positively with quality of life, especially in school (β = 0.152, p < 0.001) and associated negatively with involvement in ijime (bullying) as “victim” and “bully/victim” (β = −0.098, p = 0.001; β = −0.188, p = 0.001, respectively) and peer relationship problems (β = −0.107, p = 0.025). JaSC was found to measure school climate consistently among varying populations of Japanese students, with satisfactory validity.