So if you were having kind of a bad year your last year of junior high (for emotional or whatever reasons) - you could end up a mechanic rather than an engineer?
I'm curious as to your opinion of the system you describe?
Indeed, a bad year (either in junior high or high school) can have a huge impact on your future. There is a bit of leeway though. In some circumstances, if your teachers think that you have potential but underperformed for whatever reason, they can give you a second chance. In that case you can redo your senior year and try the national exam again at the end of that year. If your grades were never very good though and you fail the exam, they will likely direct you to a vocational/professional/technical school.
The (public) school system I attended was pretty competitive. Class rankings were very important because only the top 10% could hope to attend the best schools, so early on (5th grade for me) we were taught to constantly vie for the top spot. Even the college that I attended published class ranking to stimulate school wide competition. Where I went to school, being a "nerd" was not an insult, it was a compliment. What about people who can't compete? They are usually redirected towards alternative curriculums pretty early on. So each child's curriculum is matched to his/her abilities based on the realization that not everyone is destined to attend an ivy league school. It may sound shocking because Americans believe that all children, no matter how able, should be given the same opportunities in a public school system. Which system is better? I don't know. What I know is that, in my school system, I was always competing against the best. That, I believe, is a huge plus. Of course it can be a bitter experience for the people who get side-tracked along the way, though I found that people seem happier when they find something they can truly excel at. If math is not your thing but carpentry is, what is the point of wasting away in high school when you could learn a valuable and fulfilling craft instead? Plus, by staying in HS, you would divert resources away from people who really need them and slow everybody down. It may sound cruel, but it's true.
I have 2 cousins. School was real torture for them. I mean they really, really struggled. After junior high they were directed to vocational schools. One became an electrician, the other one a carpenter. They are now both successful in their own rights and I don't think they regret for even one moment skipping high school.
But I am sure there are some broken dreams along the way. I almost got side-tracked myself. Here is a little story:
I was a straight A student in junior high and the first 2 years of high school. Then my parents divorced and I was a bit messed up for my last 2 years of high school and my grades slipped. My goal had always been to be admitted to an elite college but based on my grades many of my teachers refused to write me important letters of recommendation. They recommended that I lowered my expectations and either applied to a public university or a technical school. I persevered nonetheless, cleaned up my act and I got a very good grade on the national exam which allowed me to be accepted in both an elite business school and an elite engineering school. I chose the engineering school from which I graduated near the top of my class with a double major, then went on to a US university where I got my Ph.D. in 4 years with a 4.0 GPA. So those 2 subpar years of high school could have cost me dearly, and I could have ended up a mechanic rather then an engineer indeed. But if I had attended high school in the US, I guess 2 years worth of so-so grades would also have damaged my higher education prospects... So I don't know if it's that different.