Actually, the original purpose and justification for tax funding for universal public schools was to educate children in citizenship in preparation for their participation in a self-governing society. The employment purpose was not a major concern in a primarily agricultural economy of independent farmers.
A republican society requires citizens who can "rule and be ruled in turn" as Aristotle first described. This was the concern of the founders and of those who proposed universal tax supported public education. Trust between citizens and observance of basic ethical principles are preconditions for a free and self-governing society to function, both in the economic sphere and as participants in self-governance.
I still believe that education for citizenship, not preparation for employment, is the best justification for taxation to support public schools in a republican society. This article indicates that our public schools, as well as the larger society, are failing in their primary responsibility of preparation for citizenship and that we, as self-governing citizens, have responsibility for allowing this to happen.