Children either excel, tread water, or fall behind. Children who fell behind once will most likely drop out of the school system entirely, unless it was for some very specific temporary reason, or their parents can afford private tutoring.
A school system that really wanted to make every child excel would probably need class sizes of 4-8, but that is well outside the realm of possibility.
1. Large class sizes are only effective if the instructional method is rote memorization. Otherwise, the teacher ends of having all the same kinds of issues corporate managers have.
2. Teachers literally go through years of formal education on pedagogy and effective leadership. Most corporate managers adhere to the Dilbert Principle, where they had been a competent IC whose role grew too big for one person, so they were allowed to hire a helper... before they know it, they're managing a team, until they become too incompetent at the managing part.
Why can't managers do what teachers do at a tenth the cost?
Like.... this isn't even the teaching part of teaching.