> what will inevitably happen is a lot of bullying.

It may not be inevitable. Personally I had pretty great experiences with multi-grade clubs, camps, sports teams, classes, academic competitions, after school programs, etc. (not to mention the neighborhood/real world.) The older kids were usually pretty nice, often really helpful, and provided a kind of role modeling.

Sports teams can sometimes be kind of hilariously unbalanced due to the drastic difference in sizes of some kids though. Perhaps some sports should be sliced into height or weight classes rather than age classes, but that's probably only practical for large leagues.

Anecdotally, as a parent, I've found the opposite to be more true. We have several schools that are k-8 in my city, but the majority split 6-8 into middle school. Talking to parents of the k-8 schools, bullying is almost non existent. Not true in the traditional middle school. Some kids are more or less mature than others as they mature, and it helps to have options for friends. Also, kids weren't split into single year age bands for all of the existence of humanity and then the past hundred years or so we suddenly split them up.

I wonder if keeping the older kids around the younger kids causes them to subconsciously inhibit their "wild teenager" behavior.

I wonder if that's an issue in many Montessori schools? What evidence do you have that bullying is a byproduct of mixed age classes?

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.

It would happen yes if the children are left on their own at that. But shouldn't we expect the school to intervene? It's not like they don't notice or they cannot know. But if the school culture says bullying is acceptable because hey that's the lead athlete and he didn't kill anybody, then yes, bullying will happen inevitably.

> But shouldn't we expect the school to intervene?

That’s a nice thing to wish, but at least in the public school system in the US, it’s no longer something that you can expect depending on the region. There are many reasons for this both including indifference and / or just being overwhelmed.

Bullying still happens among children of same age.

Children of the “same” age in school can be 11 months and 30 days apart in age. That is absolutely huge during the grade school years. In fact, month of birth is a significant factor in student athletic success. And when it comes to physical bullying, yes it’s generally the larger more physically mature kids doing the bullying.

Athletics is a pretty poor excuse for hampering a child’s education.

Athletics should be separate from schooling and run by the community (as is Europe).

"In fact, month of birth is a significant factor in student athletic success."

This was not an argument for school athletics. It was an observation that age quantization-- whether by schools or by private athletic leagues-- makes a big difference on the trajectory of athletes. In turn, you have from age quantization alone pretty big physical differences in students of the same nominal age.

Your comment is completely orthogonal to what you replied to.

Sadly sports funds large portions of some school budgets in the US. School funding is quite messed up.

Individually you feel pressure to move into the best school districts. Yet collectively it falls into racial boundaries because of decades of systemic racism.

Forced busing suddenly fixes a lot of the funding biases, but is very unpopular because fear of the other is hard to overcome.