Let's face it we have no idea how children learn so we have handled it all from experience. That was in the past. Meanwhile there was public outcry that somehow public schools were dong a bad job and besides, more importantly it was costing too much. Much of that push came from localities where people didn't want to pay enough taxes to support their schools. So a whole industry has grown up, run by people who have never taught anything to anybody, to tell us how and what to teach. and aided and abetted by colleges of "Education". These people managed to persuade politicians who they could handle the job better and at lower cost. The big thing is the money.