Put it simply, in numbers: selective schools have higher entry marks, ordinary schools lower ones.
So which is harder to prepare for? Obviously the selective one.
But the more useful question is: who is clearing that mark?
Look at who is in the room
There are certainly students from poor families who do brilliantly, and for them it genuinely changes their life. Those cases are real.
But most of the students in high-scoring schools come from households with means.
Means is what pays for extra tuition. Or simply for domestic help, so the child can concentrate entirely on studying. Or it means a parent who can be at home more.
More resources produce better results, more tutoring, better teachers. And it is that group that pushes the entry mark upward.
This does not make grades meaningless
They still reflect real effort. The people who get there have earned it.
But they are also measuring something else: how much free time you had, whether somebody else handled everything around you, whether there was money for extra hours of teaching.
Why it is worth knowing
If you did not get into the high-scoring school, do not conclude too quickly that you are worse than those who did. You may have been running the same race with considerably fewer resources.
And if you did get in, knowing that part of it was not superior ability is worth knowing too.