I heard from both my High-School history teacher and people on reddit that teenagers have a limited ability to understand history in the way for example a college graduate would. The example she gave was German feudalism, which in 9th grade (~age 15) was presented as a hierarchy with the king on top, and in 12th grade (~age 18) as a more complex system of a bargaining with several lords etc. (I'm sorry my memory might be a bit hazy on this).
Now, the point would intuitively make sense if we were talking about children who in many ways are developing faster than teenagers, but why is this still the case with teenagers, who after all have no problem comprehending other abstractions like higher mathematics or foreign languages? Is this due to neurological development, or more of a cultural thing, since a lot of our ideas about history are often molded by stereotypical or outright wrong depictions in media (or is it because of a completely different reason?).
I'm sorry if this is the wrong sub, I couldn't decide between r/Askhistorians and r/Askscience.
Could it be that 9th grade, all kids have history class so they focus on topics in less detail to cover more content, whereas in 12th grade, the kids have chosen to study history in more depth so the classes, explanations, lessons, etc. are in more detail?
I would say, completely from anecdotal experience, that younger students would get a more generalized view of history. That isn't to say it is because they are unable to understand more complex issues, but teachers want to provide a broad idea about a subject. At least in American schools, students can take AP or advanced placement courses which look at subjects with more depth than a traditional course. I imagine high school being designed as a broad introduction into all subjects and slowly allowing a student to indulge their preferences and interests through more detailed courses. There is no sense in trying to teach the complexities of feudalism to a student who prefers physics, for example. Another aspect is that history can be taught for the larger ideas behind the events and systems of the past. Teachers could try to convey grand ideas to students, instead of focusing on details. TL;DR - History teaches "big picture" ideas and details are not necessary to convey these ideas