<p>I am not sure the wheels fall off to the extent it appears.
I cannot speak for the other countries on the list, but by the time a kid is old enough to be in 11th or 12th grades in Singapore, anyone deemed in 6th grade to not have enough academic promise is no longer in conventional secondary education. They are in ‘polys’ where they are learning pre-vocational skills. So, the group of students still in the ‘academic track’ are attending what are called ‘junior colleges’ and doing their A levels or in some cases IB. </p>
<p>I suspect this is true in many places. In Australia for example, many students leave HS after 10th grade. They take the HSLC (High school leaving certificate) exam and then if they want more education they go to TAFE which is trade and vocational education.</p>
<p>My point is, the students graduating HS in the US are likely a much broader subset of all students then they are in these 2 countries., at least…</p>