1. The education of the masses reaches a minimum level of competence for 90% of the population and then stalls. Of this 90%, the lower 50% will be below the mean and hence seen as 'poorly educated'. The remaining upper 40% will fight to be seen as educated.
2. The top 10% is the limit for 'good education'. The reason is simple. As the world gets more complex, you need more educational resources to teach people enough to get along. Don't be deluded by what people seem to know—the old 'wow, kids these days know a lot of stuff' fallacy—rather, see what they do with it to change the world for the better.
3. Which leads to the next point: as the world becomes more complex, it is harder to make a clear change for the better that will affect the same proportion of the world. It will be even harder to determine if a putative change for the better is indeed a change for the better, and if so, what the cause of it was.
4. What seems to work better is not education but removal of poverty and penury. And yet again, that too has its limits—the nature of humanity is to always want to be competitive with the top 10%. Some will say that the more educated you are, the more well-off you'll be. Highly doubtful. There's a general correlation, often related to the way society (from a Marxist paradigm) values education as a way of either a) maintaining a class divide, or b) allowing people to breach the class divide.
5. The way education maintains a class divide is through labels and certifications. Some will have them, some won't. The way education allows breaches of such divisions is that most people have some chance, no matter how small, to earn such labels and certifications. But again, mass education can also be seen as a system that fosters the value (sometimes artificial and even misleading) of such things.
6. The best implementations of mass education are thus those that realise these problems and do a few things— a) set simple goals and force people to work hard and miserably to achieve them, which makes these things valuable yet attainable; b) review goals periodically and rigorously so that people don't fall too far behind a true education (i.e. world-functional) level; c) make use of turnkey systems so that even the worst teacher can deliver some crude and useful education; d) place faith in students to survive a robust delivery and teachers to provide at least some delivery; e) allow cynicism to temper the idealism so that people treat the system realistically.
Atlantean education works. It must work because it produces people able to pass every test and yet complain about everything. It produces passionate idiots and erudite genii. It is firmly normed, and normally firm. It is widely criticised and even bastinadoed (figuratively speaking) by some, but praised and emulated by others. It's a very mean system.