Classrooms with teachers, the lecture format, last made sense before the printing press.

At university, the lecturer would stand in front of the class and read a book. The students would copy the book down, because it was cheaper than paying a scribe to copy it for you, and those were the only two ways you would get your own copy of the book. The only limit to this process was how many could hear the lecturer accurately, though in practice even this distinctly drudgerous task was fairly expensive, even when split 30 ways or whatever. 

Now it's far faster, easier, and cheaper to print a copy of the lecture notes and have the students read the notes themselves. However, in the meantime lecturers had accrued social status, so we can't have that, now can we...

When not merely lecturing, but teaching, the maximum effective class size is about 4. Any bigger than that and a trained monkey with a 4-man class can do better than the top expert in the field. 

Further, hostile environments shut down the learning process. The alleged student is focusing on their enemies, not on new information, especially information that's reflexively coded as 'toy' to the savannah-issue brain. 

Or, reminder: schools are not for education. Nobody with sense tries to learn anything at school, or builds a school with the intent to teach. A tiny amount of historical literacy, or just thinking about it, scuttles the plan immediately.