It's a mistake to assume that before the 1960's, public schools were bastions of academic excellence. If you research their history, they have had problems from the very beginning.
More than any one factor, way the material is presented that is the problem. Whole-word reading instead of phonics (formerly called the alphabetic method) is just one big example. Everything is presented in a dull, repetitive, assembly-line manner, in which sitting still, being quiet, paying attention to the teacher, and waiting for permission is the core cirriculum, while developing thinking and reasoning skills aren't all that important. The educational problems we face now are simply the fruits of a schooling system the country adopted in the late 1800's. The only way to change things for the better is to stop using public schools.
Thomas Edison's mom didn't like his school, and homeschooled him.