An interesting book on this topic: Summerhill: A Radical Approach to Child Rearing

Also:

A guy tought pre-school kids how to solve linear equations. But he was an outsider so butthurt academics buried his research even though it was proven to be better:

Direct Learning, Sigfried Engelmann

https://shallteach.wordpress.com/2020/05/18/di-an-introducti...