I'm honestly not sure that the system is actually designed to discourage this (though it certainly feels like it). It's just an unintended consequence of the relatively low IQ levels of the teachers and administrators who design such systems, and the teachers who are actually doing the teaching. IQ, intelligence, call it what you will - is distributed in something approximated by a bell curve. If you had the brains to be doing advanced geometry and algebra at age 8, you are very, very likely to be smarter than virtually everyone involved in designing, administering and implementing education at any given primary or secondary school. You have an IQ that is high enough to be very rare.
There are lots of sad corollaries to this fact. Firstly, there are no resources to design an education system around a student that is 1/500, 1/1000, let alone 1/10000 in terms of rarity in the population. As soon as we approach the inverse of school population, there may not even be any student in the school who is that smart.
Secondly, it takes a smart person to understand statistics, the concept of distributions and the like. Even understanding my first two paragraphs is above the head of the average person. Due to influence of PC, its component blank slatism and the like, the number of people who both can and would even want to understand IQ, bell curves and the implications of the distribution of intelligence is even less. The ramification of this is that the vast majority of people automatically assume that anything they can't understand is either wrong or crazy, and impossible for anyone else to understand. It is insulting for many people to realize that there are problems that are too difficult for them to ever solve, but that others can solve with varying amounts of difficulty (or ease). They have an in-built chip on their shoulder towards these concepts. Most people also assume that they are smart enough to figure out who is smarter than they are, despite not realizing that there is a class of problems for which they will never, ever solve or perhaps even understand the solution, and so are incapable of judging those who will solve such things.
Then you have the problem of recruiting teachers who are capable of teaching a very bright child, if that is what you want your school system to do. There aren't any. The vast majority of the very small relative number of bright people in a given country are taking advantage of the exploitation of IQ by companies. Those who aren't duped by graduate schools into pursuing graduate education with no monetary payoff are busy earning lots of money, with job security and great working conditions. Why would they want to teach a bunch of relative dullards, when the pay is not there and the working conditions are crap? They are off doing medicine, engineering, law, business and the like.
So what do you get when your average teacher does not (want to) realize that any kid in class is smarter than they are, and can do mental gymnastics that they will never, ever achieve? And does not have the resources to allocate to it? And do not have teachers capable of teaching them? You get the current education system.
If you want to give a smart kid the opportunities to learn, you must do as the parents of the boy in this article did. You must school him yourself until he hits the point where he can autodidactically learn anything he wants to, and then give him the resources to pursue that. There is no substitute for a smart, motivated parent, involved in his child's education.