In my own experience as the beneficiary of such a system of education - the barrier is having to pass admission exams that are meant to ensure that available spaces are offered to those academically inclined to succeed.
In my personal circle of acquaintances all who were interested in securing the spot were able to do so.
But in an event you fail, you have an option to work on your shortcomings and take the admission exams again.
In my own experience as the beneficiary of such a system of education - the barrier is having to pass admission exams that are meant to ensure that available spaces are offered to those academically inclined to succeed.
In my personal circle of acquaintances all who were interested in securing the spot were able to do so.
But in an event you fail, you have an option to work on your shortcomings and take the admission exams again.