@Cesca It depends on many factors, but very bluntly said: intelligence and motivation.
When they stop at 16, that's called VMBO; they can go to some sort of college that prepares them for 'lower' (don't mean to insult anyone, worked as a nanny and a cleaner myself during my teen/uni years
) jobs like a hairdresser, cleaner, etc.
When they stop at 17, "Havo", they can do higher jobs, like a teacher etc, but not university
When you stop at 18, "Vwo", that's usually for the brightest kids that can handle the most difficult schooling. It prepares you for university with the intention for them to be something like a lawyer, doctor, etc.
I hope that explains it a litty! It's hard to explain when it's so 'normal' for me, like explaining how to walk XP
It depends though; to be an elementary school teacher you don't need uni, but for a secondairy school teacher I think you do (like, if you're a French teacher you'll need to have studied French, for instance). Although they accept lower educations too now that there's a huge shortage of teachers lol... Not so good on the schooling system XP
Linear Mode
