I'm new here, and I'm just gonna write this for fun.
Consider this, in the near future, where humans have advanced much in the field of computing power and data collection. Scientists can run simulations with artificial intelligence that would enable machines to be trained in undertaking tasks that are considered too complicated to do for our current computing standards.
In such a world, most jobs becomes depreciated, because machines can perform pretty much all the tasks. People can afford to live without jobs (or money), one can just go pickup their daily needs (produced by machines) such as food or any other product from some local warehouse.
It it then much better if you have a majority of less educated people.
For starters, it would be important to keep close control over the boundaries of AI development. Someone has to to make sure AI doesn't evolve in ways which would harm our existence. Those people needs to be highly educated and responsible (mostly responsible). And you just need a small number of such people (possibly monitored closely) so their actions are easily controlled.
This would be opposed to where if most people have high education, then you'd have no control over how AI might evolve. Some high school kid could be running a simulated virtual organism on his home computer, feeding it random data from the internet (or whatever more advance version we'd have in the future), without proper limitation on how it might evolve. Before long, people would be creating dangerous AI programs that would threaten our existence.
It would be better then, if say only 1% of people receive high enough education that would allow them to evolve and control the computers software. And the other 99% are only smart enough to happily play candy crush or posting selfies on facebook.
The other reason would be social unrest. When the computers take over our jobs. You'd be left with a lot of bored people. As it turns out, higher educated people are much harder to satisfy.
Ideally, people should be holidaying forever and spending more time to explore arts and music or their other none dangerous hobbies. But this only happens if they are dumb. e.g. people in the middle ages would be happy if all they did was partying and having sex forever, they'd even be happy if they worked as a blacksmith at the same place forever. But an educated person would be bored out of their mind. They'd be seeking ways for intellectual stimulation (such as the challenge of making killer robots, protesting and starting revolutions).
Lastly, why would you even need to educate people, 99% of the jobs would be taken care of, and it would be a waste of time and resources to train people when it would be better for everyone to be stupid. Sure, social values would probably degrade pretty soon, but it'd be a better alternative than total self destruction.
This might actually happen, think about it and have a nice day :).
Interesting point from @inappropriateCode with the human urge to teach and learn. One would think it'd surely be hard to enforce restrictions on education, especially in an advanced future society. But maybe this isn't as far fetched as it may seem. It might actually happen naturally to some extend.
Just to clarify, the machines in my proposed situation would be smart enough to carry out structured jobs efficiently. Say to design and 3D print cars, grow crops to the best yield. But maybe not efficient enough to run an program that trains an AI to "freely reason", in any manageable time.
The main motivation for a government who wants to dumb the population down would be to reduce the chances of someone from creating such AI programs (in which case it could force a man vs machines intellectual arms race which we'll probably lose because the human brain evolves slower).
It might take a few generations from now to reach that point. In which time people are going to get less dependent on having a job to make a living.
At some point (even now, in some countries) jobs becomes optional, and a percentage of the population would choose to not get a job or an education, as the "jobless living standards" improve, more and more people would fall into this category. And their kids would grow up in an education optional lifestyle, with no particular reason to break out of this bubble.
After some time, you'd be left with the fairly intellectually minded people, that would still choose to get an education. Now the government decides to give the dumbing process a nudge, it impose a high education fee. Remember that pretty much all the young people at this point would be born in to a job and education optional world, so unless if you're very motivated, you probably wont fight against it. Maybe most people would be redirecting their attention to some other none formal education required activity, such as arts and craft, to fulfill their intellectual needs.
We're now left with the really motivated people, who still wants to get formally educated, but even if they can pay the fees, they'd have to study really hard, with less teaching resources, and the seriously advance shit they'd have to learn. Their reward for finishing their studies would be to monitor the world and keep the machines in check (that'd pretty much be the only jobs available), while everyone else gets to party none stop or do whatever the hell they feel like.
The ones that can't afford to study but still wants to can do home learning and or form interest groups (it's their right, why not?). But if the government ban free access to teaching resources and compiling software for computing. You'd have seriously hard time trying to design code / hack into the system from scratch. Remember technology would be more advance in the future which increases the difficulty. While you're trying hack your way into AI advancement, you'd surely standout from everyone else and the government can put a stop to it before you become a problem. In that sense, there's no real need for the government to ban learning, plus you'd be fine if you don't touch AI, just learn accounting instead, that's like....fun too....
And if you've received a formal education and decides to not get a job after, you'd still have the restricted access to computing resources and you'd be watched for life probably. All manageable problems.
So there you go, that's how humanity would devolve in an advanced world, don't take it seriously..... but it might happen.....