None, because it’s not common. All I know is that research shows that bullying develops and evolves by age. It’s not going to be as prevalent in early age Montessori schools as it is in middle school. Let’s also not ignore that a private Montessori school is also a filter.

Do you have any cite for your research about bullying and mixed-age?

I have already told you it doesn’t exist for mixed ages because it’s not a common situation. The closest thing to it are papers noting at what ages bullying tends to occur and the nature of said bullying.