My daughter is very bright and maybe even top 3 in her class (though the teacher would have never given me this info if I'd asked!)... she's naturally good at maths and English, excellent memory, good at logic puzzles and loves learning... but despite the prep we did at home, missed out by 2 marks.
I started gently in y4 with a few papers and exercises, then at the end of y4 I got a tutor weekly... in y5 I ramped up the prep to 20 mins daily and weekly tests.... but despite this she didn't make it.
Those who did make it had done even more tuition than us, more hours per week over a longer period of time.
On the day of the test, there were soooo many girls... I knew it would be competitive but I had no idea how much.
If your daughter is a Sept born child, you will need to get them to aim even higher in the test as the results are age adjusted. I think this is what got us... we were aiming for a certain mark as a raw score (80%) but we needed to aim for 90% really.
I don't know if we would have still gone through all of that, knowing what I know now... or if we would have gone for it but taken a different approach... I do wish I'd known more about it though!
It all worked out in the end as she loves her school... and I know her sisters will go to the same school as her too (they're not as academic anyway, so this is a weight off!).