Bullying is a substantial problem in schools worldwide and it can have severe consequences for individuals in both short and long-term. One aim of this study was to explore the bullying prevalence among 10-year-olds in school-systems participating in TIMSS 2015. Another aim was to examine the variability in bullying prevalence across schools in the participating countries to, finally, explore how school-related factors could reduce bullying prevalence. The main method was multilevel modeling. Overall, the results showed relatively high bullying prevalence even though the variability was large among the 50 countries. Some countries had substantial school differences and these were selected for further scrutiny. While socioeconomic status did not impact on bullying prevalence in a sub-sample of countries, factors like school climate and a sense of school belonging had an effect in most of them. Implications of the results were discussed.