I've answered similar questions on this topic that should hopefully get at what you're wondering about. I'm happy to answer any follow up questions you might have; UrAccountabilibuddy is my old username.

• Why does the USA have 3 tiers of education (elementary, middle high) whereas countries like the U.K. have 2 (primary, secondary)
• what do we know about the original purpose of the rise of tax-paid, compulsory schooling that became widespread?
• When did we start making kids sit down in school?