In the 1900s the idea of education for the masses emerged. Previously, only the rich and near rich went to school. The poor. if very motivated, with some kind of sponsor, might be able to attend.
The idea of teaching average and poor people how to read and write and do sums was rather revolutionary. The general belief was that the lower class didn’t need to think, they needed to work.
Educating the lower classes became standard. Children in the 1920s went to school. It could be an ‘All Age’ which ended at fourteen, but it was a school, and the child was literate. Although not mandatory, education was encouraged.
In the 1940s education became a bit more important and by the 1950s the push for higher education, (due to the Cold War) was strong. This focus on education lasted deep into the 1970s.
But the fact is, an educated underclass refuses to be an underclass. An educated population will not blindly follow a leader, will not agree to policies which are designed to bring wealth into the pockets of millionaires and not benefit the majority.
For working class people to be able to send their children to University was blasphemy for the rich, so education has been dismantled. Schools are modified and what information is dispensed of limited value.
Dystopian novels explain how populations of average people are turned into mindless sheep. Whether brain damage is performed before or after birth.
There can be no 1984, no Brave New World, no Idiocracy, unless the population has been dumbed down.
This is why, since the 1970s the process dumbing down has been implemented.