A teacher needs to know their students to be effective. This puts an upper limit on the number of students one teacher can teach at once. Something like 150 students. I need to know their names, and when I see that name a little about who that is.
Further, a student should have at least 4 or 5 teachers who know them. This is a selection of hopefully trustworthy and supportive adults they can turn to.
Most plans to make school less expensive mess with these numbers.



