Schools were designed by Horace Mann and Barnard Sears and Harper of the University of Chicago and Thorndyke of Columbia Teachers College and some other men to be instruments of the scientific management of a mass population. Schools are intended to produce through the application of formulae, formulaic human beings whose behavior can be predicted and controlled.
Grades don't measure anything other than your relevant obedience to a manager.
Do we really need school? I don't mean education, just forced schooling: six classes a day, five days a week, nine months a year, for twelve years. Is this deadly routine really necessary? And if so, for what? Don't hide behind reading, writing, and arithmetic as a rationale, because 2 million happy homeschoolers have surely put that banal justification to rest.
Government schooling made people dumber, not brighter; made families weaker; ruined formal religion with its hard-sell exclusion of God; set the class structure in stone by dividing children into classes and setting them against one another; and has been midwife to an alarming concentration of wealth and power in the hands of a fraction of the national community.
It is absurd and anti-life to be part of a system that compels you to listen to a stranger reading poetry when you want to learn to construct buildings, or to sit with a stranger discussing the construction of buildings when you want to read poetry.
God was pitched out of forced schooling on his ear after WWII. This wasn't because of any constitutional proscription-there was none that anyone had been able to find in over a century and a half-but because the political state and corporate economy considered the Western spiritual tradition too dangerous a competitor. And it is.