Why 69 years?
1945,the end of WWII. From that point on, slowly but with increasing pressure the dumbing down of the children began.
Oh wait! They would have been graduates of the newly established K-12 compulsory-use, single-payer, and socialist-entitlement schools!
SS schools ( Single-payer and socialist-entitlement schools)
According to Reagan's former Undersecretary of Education, Charlotte Thompson Iserbyt's book, the deliberate dumbing down of america, it was long before that, but the realms in which it was accomplished were selective.